An abnormality detection device is mounted on an engine control device that calculates a target load factor by using a target torque, converts the target load factor to a target throttle opening, calculates a target ignition timing by using a target efficiency, and controls an engine based on the target throttle opening and the target ignition timing. In the abnormality detection device, a target efficiency for monitoring is calculated by using the target ignition timing, a target torque for monitoring is calculated by using the target efficiency for monitoring and the target load factor, a torque deviation between the target torque for monitoring and the target torque is calculated, and the presence or absence of an abnormality is detected by using the torque deviation.