PURPOSE: To omit correcting operation based upon a wrong input signal by providing an operation inhibiting means which inhibits the operation of an input means.

CONSTITUTION: An input key 2, input stop key 3, etc., are provided on a keyboard 1, and an encoder circuit 4 which encodes data, etc., is provided. The encoded signal is ANDed by an AND circuit 5 and inputted to a signal processing part 6. A printer 7, etc., are connected to the signal processing part 6, and ROM6b stored with a program necessary for the arithmetic processing of the input signal, CPU6c which performs specific signal processing, etc., are provided. When the operation is interrupted, the input stop switch 3 is turned on and a password is inputted with input keys 2; and processing is performed by the signal processing part 6 to inhibit all operation, and the execution is inhibited thereafter even if a command, data, etc., are inputted on the keyboard 1.