permit the switch 22 to be in off state upon further depression of the drive piece 16 the drive piece 16 is now pivoted in clockwise direction against the spring 27 on the movable contact portion 25a of the switch 21 as the drive piece 16 is thus rotated the cushion member 18 will depress the movable contact piece 29a of the switch 22 to cause the switch 22 to become in on state similarly to the switch 21 as described above as shown in fig4 b therefore both the switches 21 and 22 are closed on in this state the time period t from the time point when the switch 21 becomes on as in fig4 a to the time point when the switch 22 becomes on as in fig4 b thus varies in accordance with the rotating speed of the drive piece 16 it is to be noted that in cause wherein excessive depressing pressure is applied to the drive piece 16 the cushion members 17 and 18 will absorb this pressure so as to protect the switches 21 and 22 together with the drive piece 16 being prevented from bounding upon release of the depressing pressure on the drive piece 16 the.