PURPOSE: To enable clock abnormality to be judged at a low expense in the controller of a vehicle, provided with a clock generating circuit for generating periodic pulses.

CONSTITUTION: Pulse voltages at specific time intervals produced on the basis of clock pulses are inputted into a time constant circuit 12 comprising a resistance R and a capacitor C. Then, presence of clock abnormality is judged when the voltage of the capacitor C is inputted into a microcomputer 2 and an input voltage at a specific sampling time gets out of a specific range.