A message conversion system converts a message regarding one operation screen out of an operation screen after the customization and a default screen before the customization to a message regarding the other operation screen, and includes: a first obtainer that obtains a name of the operation item and identification information of operation control; a second obtainer that obtains a name of the operation item and identification information of operation control; a creator that creates a comparison table; and a replacer that specifies the identification information corresponding to the name of the operation item included in the message regarding one operation screen, and obtains the name of the operation item of the other operation screen and replaces the name of the operation item of the one operation screen included in the message with the name of the operation item of the other operation screen.