A program managing method in a web service system for providing a web service for testing a message which has been changed in response to a change made in interface definition information comprises steps for judging as to whether or not an error occurs when an access request made by a message is transmitted, which is caused by the change of the interface definition information indicative of an interface of a destination of the access request; changing the message in correspondence with a content of the changed interface definition information in the case that the error occurs which is caused by the change of the interface definition information; and transmitting an access request made by the changed message in a test mode. It then becomes possible to correct and test the program in a dynamic manner for preventing recurrence of this error.