An apparatus detects positions of the right/left and front/rear four wheels of a vehicle. The detection is performed using transceivers attached to the respective wheels, a triggering device disposed in a body of the vehicle to output the triggering signal, and a receiver disposed on the body. The triggering device includes a first triggering device located closer to the two front wheels than thetwo rear wheels and located at a position where distances from the right-Front wheel and the left-front wheel are mutually different, and a second triggering device located closer to the two rear wheels than the two front wheels and located at a position where distances from the right-rear wheel and the left-rear wheel are mutually different. Distances between each triggering device and each of the two transceivers receiving the triggering signal from the triggering device are decided at a given ratio in consideration of reception sensitivity.