PURPOSE: To conduct or cut off a current by shifting an iron wire switch ring which is slidably drawn along the inner periphery of a steering wheel under the influence of a grasp thereof, thereby preventing a driver from being asleep by an alarm when the current is conducted.

CONSTITUTION: When a driver grasps a steering wheel 1, either an upper iron wire switch ring 18 or a lower iron wire switch ring 21 is pulled to compress a coiled spring 20 so that a flange 19 is removed from a contact 16 to cut off a current to a lamp 6 and a buzzer 4, that is, the lamp comes off and the buzzer is halted. If the driver, asleep during driving, relaxes his attention and loosens his grasp down to a certain pressure or less, the coiled spring 20 is returned to push the flange 19 into contact with the contact 16 so that the electrification lamp 6 is lit and the buzzer 4 is alarmed for the driver.