Hi everyone :) I use logback-access instead of tomcat default valve. Using logback version is 1.1.3. I use logback-core-1.1.3.jar, logback-classic-1.1.3.jar. When use logback-access-1.1.3 at the same time, tomcat puts error. :( %b pattern output is so weird. First, i use class "ch.qos.logback.access.tomcat.LogbackValve" Pattern is this. [%t]\t%U\t%s\t%D\t%b Second, i use class "org.apache.catalina.valves.AccessLogValve" Pattern is this. %t	%U	%s	%D	%b I think they are same. So, try using same time. But "%b" pattern output was different. This is example. First, Logback. [02/Jun/2015:20:12:28 +0900] /test/testLayout.css 200 366 - Second, Tomcat valve. [02/Jun/2015:20:12:28 +0900] /test/testLayout.css 200 367 2769 Logback's output is "-" but Tomcat is "2769" I think Tomcat valve's value is correct. Why they are different? Please tell your advice. Best regards, Aristein.