An abnormality detection device includes a processing circuit configured to perform an abnormality detecting process. The abnormality detecting process includes a first state quantity acquiring process, a second state quantity acquiring process, a difference calculating process of calculating a difference between a first state quantity and a second state quantity, and a determination process of comparing an absolute value of the difference with a difference threshold value. The abnormality detecting process is a process of detecting an abnormality of a turning unit when the absolute value of the difference is greater than the difference threshold value, and the processing circuit is configured not to perform the determination process when an absolute value of an actual current value is greater than a current threshold value.