diff --git a/CHANGELOG-Japanese.md b/CHANGELOG-Japanese.md
index fddd88ded..868c5e4a9 100644
--- a/CHANGELOG-Japanese.md
+++ b/CHANGELOG-Japanese.md
@@ -7,6 +7,7 @@
 - 指定した`status`のルールのみを利用する`--include-status`オプションを追加した。 (#1193) (@hitenkoku)
 - 未使用のクレートを削除した。(@YamatoSecurity)
 - SplunkからエクスポートしたJSONファイルの入力に対応した。 (#1083) (@hitenkoku)
+- パフォーマンスの改善 (#1277, #1278) (@fukusuket)
 
 **バグ修正:**
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c97ab8553..68a9cec89 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,8 @@
 
 - Added `--include-status` option: You can specify rules based on their `status`. (#1193) (@hitenkoku)
 - Removed unused crates. (@YamatoSecurity)
-- Adjusted JSON input file exported from Splunk. (#1083) (@hitenkoku)
+- JSON input now supports the format exported from Splunk. (#1083) (@hitenkoku)
+- Performance enchancements. (#1277, #1278) (@fukusuket)
 
 **Bug Fixes:**
 
diff --git a/src/detections/rule/aggregation_parser.rs b/src/detections/rule/aggregation_parser.rs
index bfe985d18..2b6d52fdc 100644
--- a/src/detections/rule/aggregation_parser.rs
+++ b/src/detections/rule/aggregation_parser.rs
@@ -88,29 +88,29 @@ impl AggegationConditionCompiler {
         &self,
         condition_str: String,
     ) -> Result<Vec<AggregationConditionToken>, String> {
-        let mut cur_condition_str = condition_str;
+        let mut cur_condition_str = condition_str.as_str();
 
         let mut tokens = Vec::new();
         while !cur_condition_str.is_empty() {
             let captured = self::AGGREGATION_REGEXMAP.iter().find_map(|regex| {
-                return regex.captures(cur_condition_str.as_str());
+                return regex.captures(cur_condition_str);
             });
             if captured.is_none() {
                 // トークンにマッチしないのはありえないという方針でパースしています。
                 return Result::Err("An unusable character was found.".to_string());
             }
 
-            let mached_str = captured.unwrap().get(0).unwrap().as_str();
-            let token = self.to_enum(mached_str.to_string());
+            let matched_str = captured.unwrap().get(0).unwrap().as_str();
+            let token = self.to_enum(matched_str);
 
             if let AggregationConditionToken::Space = token {
                 // 空白は特に意味ないので、読み飛ばす。
-                cur_condition_str = cur_condition_str.replacen(mached_str, "", 1);
+                cur_condition_str = &cur_condition_str[matched_str.len()..];
                 continue;
             }
 
             tokens.push(token);
-            cur_condition_str = cur_condition_str.replacen(mached_str, "", 1);
+            cur_condition_str = &cur_condition_str[matched_str.len()..];
         }
 
         Result::Ok(tokens)
@@ -226,7 +226,7 @@ impl AggegationConditionCompiler {
     }
 
     /// 文字列をConditionTokenに変換する。
-    fn to_enum(&self, token: String) -> AggregationConditionToken {
+    fn to_enum(&self, token: &str) -> AggregationConditionToken {
         if token.starts_with("count(") {
             let count_field = token
                 .replacen("count(", "", 1)
@@ -248,7 +248,7 @@ impl AggegationConditionCompiler {
         } else if token == ">" {
             AggregationConditionToken::GT
         } else {
-            AggregationConditionToken::Keyword(token)
+            AggregationConditionToken::Keyword(token.to_string())
         }
     }
 }
diff --git a/src/detections/rule/condition_parser.rs b/src/detections/rule/condition_parser.rs
index 2ed2c9621..c0d8c4dde 100644
--- a/src/detections/rule/condition_parser.rs
+++ b/src/detections/rule/condition_parser.rs
@@ -91,7 +91,7 @@ impl ConditionToken {
         };
     }
 
-    pub fn to_condition_token(token: String) -> ConditionToken {
+    pub fn to_condition_token(token: &str) -> ConditionToken {
         if token == "(" {
             ConditionToken::LeftParenthesis
         } else if token == ")" {
@@ -105,7 +105,7 @@ impl ConditionToken {
         } else if token == "or" {
             ConditionToken::Or
         } else {
-            ConditionToken::SelectionReference(token)
+            ConditionToken::SelectionReference(token.to_string())
         }
     }
 }
@@ -130,7 +130,7 @@ impl ConditionCompiler {
         let captured = self::RE_PIPE.captures(condition_str.as_str());
         let replaced_condition = if let Some(cap) = captured {
             let captured = cap.get(0).unwrap().as_str();
-            condition_str.replacen(captured, "", 1)
+            condition_str.replace(captured, "")
         } else {
             condition_str.to_string()
         };
@@ -191,28 +191,28 @@ impl ConditionCompiler {
 
     /// 字句解析を行う
     fn tokenize(&self, condition_str: &str) -> Result<Vec<ConditionToken>, String> {
-        let mut cur_condition_str = condition_str.to_string();
+        let mut cur_condition_str = condition_str;
 
         let mut tokens = Vec::new();
         while !cur_condition_str.is_empty() {
             let captured = self::CONDITION_REGEXMAP.iter().find_map(|regex| {
-                return regex.captures(cur_condition_str.as_str());
+                return regex.captures(cur_condition_str);
             });
             if captured.is_none() {
                 // トークンにマッチしないのはありえないという方針でパースしています。
                 return Result::Err("An unusable character was found.".to_string());
             }
 
-            let mached_str = captured.unwrap().get(0).unwrap().as_str();
-            let token = ConditionToken::to_condition_token(mached_str.to_string());
+            let matched_str = captured.unwrap().get(0).unwrap().as_str();
+            let token = ConditionToken::to_condition_token(matched_str);
             if let ConditionToken::Space = token {
                 // 空白は特に意味ないので、読み飛ばす。
-                cur_condition_str = cur_condition_str.replacen(mached_str, "", 1);
+                cur_condition_str = &cur_condition_str[matched_str.len()..];
                 continue;
             }
 
             tokens.push(token);
-            cur_condition_str = cur_condition_str.replacen(mached_str, "", 1);
+            cur_condition_str = &cur_condition_str[matched_str.len()..];
         }
 
         Result::Ok(tokens)