PURPOSE: To obtain a general-purpose debugger by having comparison between the back link pointer value in the task state display addressed by a task register and the designated prescribed value and neglecting the interruption given from an address stop interruption generator in case the result of said comparison does not satisfy the designated conditions.

CONSTITUTION: A task A to which a debugger task DBG gives an interruption is recognized by means of the value of a task register TR (A), the value of the task state display TSS (A) and a back link pointer RLP. Then it is previously judged whether the task A is equal to a desired task to be debugged or not by means of an identifier for task to be debugged (task register value) that is previously designated by a debugger and the comparison conditions. Then the start of the debugger is decided. While a task resuming instruction is produced to continue the processing of the task A if this task A does not satisfy the desired conditions.