To provide an object-oriented design support device capable of showing behavior of an object by a diagram, and describing an action executed in the behavior by a programming language.

In this object-oriented model design support device, a list of events capable of being sent by an optional object is produced from information of a class diagram, and priority is imparted to the transmittable event from information of a sequence diagram in the list. The action description wherein a letter string has been inputted one letter by one letter heretofore can be inputted by a selection form, and a selection item can be displayed in favor of an item having strong possibility of input, so that the description of the action becomes easy.