PURPOSE: To effectively extract information effective for specifying error on a program by providing a stack for recording an operating state for each program and providing a debugger module for extracting the operational history of the program form this stack, reloading this history and further outputting it.

CONSTITUTION: The middle state of executing the program is held and managed by the stack provided on a memory 2 corresponding to each module so as to hold the executing state of the program. Each time the program module is executed, one stack frame SF is generated. Therefore, when plural programs are executed, a high-order master frame SF1 and a slave frame SF2 activated by the master frame SF1 are activated, this slave frame SF2 are turned to the master frame, and a slave frame SF3 is activated. Thus, the execution history of modules is discriminated by following the contents of continuous stack frames.