PURPOSE: To make an alarm sound one time every 24hr by a method wherein an inversion circuit to invert an output state by a signal indicating the coincidence between an alarm time and an ordinary time every 12hr and then, an alarm is driven by the output.

CONSTITUTION: When coincidence between an ordinary time display part 5 and an alarm time display part 7 is detected 9, the output passes through a chattering elimination circuit 10 and is applied to an inversion circuit 13. As the inversion circuit 13 inverts its state every time when this signal b is applied, an output f becomes "1" one time every two times of the signal b, thus, an alarm driving circuit 11 driving an alarm 12 once every 24hr.