| 摘要 |
An inflation pressure sensor is mounted in a wheel of a vehicle and determines a tire inflation pressure. A wheel-side communication device transmits a detected tire inflation pressure to a body-side communication device at a predetermined interval. An inflation pressure storing unit stores, as an after-travel inflation pressure, a tire inflation pressure after start of travel of the vehicle. A comparing unit compares the after-travel inflation pressure with a lowest reference pressure. The lowest reference pressure is a tire inflation pressure immediately after start of the vehicle or a predetermined recommended inflation pressure. A reference pressure setting unit sets the after-travel inflation pressure as a reference pressure of tire inflation pressure determination when the after-travel inflation pressure is higher than the lowest reference pressure, and sets the lowest reference pressure as a reference pressure of tire inflation pressure determination when the after-travel inflation pressure is equal to or lower than the lowest reference pressure. When the tire inflation pressure becomes below an alarm pressure threshold obtained from the reference pressure, an alarm unit generates an alarm.
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