Provided is a parking space detector designed so as not to erroneously detect an inter-vehicle distance as a parking space, the inter-vehicle distance being the distance between oncoming vehicles continuously passing by. The invention is provided with a parking space presence determination part for determining whether or not a parking space for a vehicle is present. The parking space presence determination part is designed so as to determine whether or not oncoming vehicles are stationary on the basis of the vehicle speed and the relative speed of the oncoming vehicles, therefore preventing the space (inter-vehicle distance) between two other oncoming vehicles being erroneously detected as a parking space, the oncoming vehicles being vehicles traveling toward the vehicle and continuously passing by.