A device to accurately identify the wheel position where each tire has a radio wave transmitter installed without special means or operation during application by using a simple and compact configuration. This TPMS has sensor modules 14A, 14B, 14C, 14D on the transmission side equipped by tires 12FL, 12FR, 12RL, 12RR installed on automobile 10 and main device 16 on the receiving side loaded in automobile 10. Main device 16 is comprised of a group of two antennas 18, 20, receiver 22, and display 24. Two antennas 18, 20 are arranged appropriately to receive the radio waves transmitted by each of sensor modules 14A-14D with a phase difference between them.