PURPOSE: To conversationally and visually develop a window control function by displaying a window of the processing object on a screen and converting the operation for the window to an event and activating the event processing tool thereafter.

CONSTITUTION: An event taking-out device 1 takes out an event stacked in an application event queue and delivers it to a window control function determining device 2. This device 2 determines a correspondent window control function in accordance with the received event and refers to a window control function table 3 to deliver the index of the correspondent window control function to a window control function distributing device 4. The device 4 delivers the received index to a window control function editor 5, a window control function executing device 6, or a window control function debugger 7 in accordance with a preliminarily set mode. Thus, the window control corresponding to some event is edited to perform control and debugging on the screen.