To abolish measurement in a constant time interval at stopping time, and to avoid useless battery consumption by measuring tire inflation pressure even in a low speed travel state just after starting travel of an automobile.

This tire inflation pressure sensor composed of a pressure sensor for detecting tire inflation pressure, a travel sensor for detecting travel, an electronic circuit part for transmitting detecting pressure to a car body side receiver by a radio wave and a battery for actuating the electronic circuit part, is so constituted that the travel sensor is formed out of a moving body 6 and a piezoelectric element 7, the electronic circuit part discriminats a period of voltage generated when the moving body 6 collides with the piezoelectric element 7 by rotation of the tire to start the travel when the period becomes short, and to stop the travel when the period becomes long.