An object detection circuit detects an object moving in a periphery of a vehicle by a frame correlation method that uses a plurality of shot images captured at successive times. A state judgment part disables a detection function of the object detection circuit when a steering angle of an own vehicle is not in a prescribed steering angle range. Then, a condition changer changes the prescribed steering angle range corresponding to a condition of the steering angle in accordance with a velocity of the own vehicle. Therefore, the condition changer can relax the condition for enabling the detection function in accordance with the velocity of the own vehicle within a range where detection accuracy is ensured.