PURPOSE: To facilitate the debugging of multi-task by synchronizing the permission or the inhibition of the execution of plural tasks belonging to the same job group.

CONSTITUTION: A task assigning mechanism attaches the same task group identification name to the tasks belonging to the same task group, and permits or inhibits the execution of the task according to the value of the same dispatching control flag 5220. When the optional task in the group reaches a break point, the execution of all the tasks is inhibited by turning the dispatching control flag 5220 into an inhibition state, and issuing an interruption request to the tasks under execution having the same task group identification name. After the debugging, the dispatching control flag 5220 is turned into a permission state so as to enable the re-execution of the task.