PURPOSE: To prevent a processing hot intending to execute from being performed accidentally by enabling an arbitrary command to be inputted as a command to limit execution and a limited state to be cancelled arbitrarily by a user.

CONSTITUTION: When the user inputs the command not intending to execute by using an input device 6 at need, a limitation command setting means 1 makes a part AR4 in a limitation command storage means RAM4 store the command. In the above state, the limitation command processing prohibition means 1 prohibits the execution of the command even when the command is inputted. Also, in the case of cancelling the limitation of the command whose execution of the processing is limited, the user inputs the command to cancel the limitation by using the input device 6. At such a time, the limitation command cancellation means 1 deletes an inputted command from the commands stored in the limita tion command storage means AR4. In such a way, it is possible to prevent the processing of an unrequired command from being executed.