An electronic control device according to an embodiment of the present invention includes an arithmetic device such as a microcomputer having a watchdog timer circuit, and a runaway monitoring circuit which monitors the arithmetic device for an operational failure by receiving a pulse output from the arithmetic device, in which the watchdog timer circuit or the runaway monitoring circuit detects occurrence of a failure of the arithmetic device according to the state (high level or low level) of an indication signal (wakeup signal) which shows the operational state of the arithmetic device.