PURPOSE: To set a penalty time during which no re-input of an input code is accepted according to the number of inputs of mistaken input codes.

CONSTITUTION: Detection is made by a comparative means 12 whether or not an input code agrees with an identification code, and when these codes agree with each other, a car audio device is set in the operable mode. The data of the times of detection of such a condition that the input code and the identification code do not agree with each other is set to be written in a times memorizing part 9, and the time which is measured by a timer means 14 according to the previous times data is changed. And an arrangement is made so that no re-input of the input code may be accepted until the time measurement is completed by means of the timer means 14, and the time not to accept the re-input of the input data is extended according to the times of the inputs of the mistaken input codes. The times memorizing part 9 is composed of a non- volatile memory so that the previous times data may no be erased even when the power supply is shut off.