An abnormality detection device configured to detect an abnormality of a turning unit including a motor that is a drive source, a turning shaft that is connected to turning wheels, a power transmission mechanism configured to transmit a torque of the motor to the turning shaft, a first sensor configured to detect a rotation angle of the motor, a second sensor configured to detect a conjunction state quantity indicating position information on a conjunction member that is mechanically connected to the motor via the power transmission mechanism, and a current sensor configured to detect an actual current value that is a value of an actual current supplied to the motor, the abnormality detection device comprising: a processing circuit configured to perform an abnormality detecting process, wherein the abnormality detecting process includes a first state quantity acquiring process of acquiring a first state quantity indicating position information on a convertible member based on the rotation angle detected by the first sensor, the first state quantity being convertible to a turning angle of the turning wheels; a second state quantity acquiring process of acquiring a second state quantity indicating position information on the convertible member based on the conjunction state quantity detected by the second sensor; a difference calculating process of calculating a difference between the first state quantity and the second state quantity; and a determination process of comparing an absolute value of the difference with a difference threshold value, wherein the abnormality detecting process is a process of detecting the abnormality of the turning unit when the absolute value of the difference is greater than the difference threshold value, and characterized in that the processing circuit is configured not to perform the determination process when an absolute value of the actual current value is greater than a current threshold value. a processing circuit configured to perform an abnormality detecting process, wherein the abnormality detecting process includes a first state quantity acquiring process of acquiring a first state quantity indicating position information on a convertible member based on the rotation angle detected by the first sensor, the first state quantity being convertible to a turning angle of the turning wheels; a second state quantity acquiring process of acquiring a second state quantity indicating position information on the convertible member based on the conjunction state quantity detected by the second sensor; a difference calculating process of calculating a difference between the first state quantity and the second state quantity; and a determination process of comparing an absolute value of the difference with a difference threshold value, a first state quantity acquiring process of acquiring a first state quantity indicating position information on a convertible member based on the rotation angle detected by the first sensor, the first state quantity being convertible to a turning angle of the turning wheels; a second state quantity acquiring process of acquiring a second state quantity indicating position information on the convertible member based on the conjunction state quantity detected by the second sensor; a difference calculating process of calculating a difference between the first state quantity and the second state quantity; and a determination process of comparing an absolute value of the difference with a difference threshold value, wherein the abnormality detecting process is a process of detecting the abnormality of the turning unit when the absolute value of the difference is greater than the difference threshold value, and characterized in that the processing circuit is configured not to perform the determination process when an absolute value of the actual current value is greater than a current threshold value.