A tire attaching position detection system is provided which can suppress influence by an intensity of a reception signal from a tire. In the system, a sensor unit is mounted on each tire, the sensor unit has a geomagnetic sensor for acquiring data on direction change of the tire, a distortion sensor for acquiring data on number of rotations of the tire and a transmitting part for transmitting the direction change data and number of rotations data of the tire. A calculation part of a user terminal judges the attaching position of each tire based on the direction change data and the number of rotations data of each tire transmitted from the transmitting part.