A control device with a time measuring function measures a turned-off time of an ignition switch with a low consumption current and high accuracy at a level adapted for a demand from the controlling side, as well as a turned-on time of the ignition switch. The control device also measures an accumulative turned-on time of the ignition switch. The control device comprises a battery, a microcomputer for computing a control variable to control a control target, a time measuring unit, a clock source for the microcomputer, a clock source for the time measuring unit, and a unit for changing over operation of the time measuring unit depending on an intended use. The time measuring unit operates regardless of run/stop of the microcomputer.