PURPOSE: To reduce noises by providing a spiral groove on the surface of a gear which is rotated by a driving motor, driving a movable indicating plate which moves linearly, and indicating the computed operation hour of the timer.

CONSTITUTION: An engaging knob 18 which is provided on the linearly moving movable indicating plate 13 is engaged with the spiral groove 12a provided on the surface of the rotating gear 12, which is driven by the torque of the driving motor. The amount of the movement of the indicating plate 13 can be observed through an observing window 14a and the operating hour of the timer is computed and indicated. Since the engaging knob is merely slidden in a center 12a1 of the spiral part 12a even at a warning position, the noises are not generated.