To provide a revolution sensor by which the rotational speed of a tire can be counted with good accuracy and by which a usage state can be monitored properly by a method wherein a force sensor is disposed at a rigid base body and a countable output signal is generated.

A rigid base body 1 which is used as a mounting base is installed on the inner face I in the radial direction of a tire tread, and a force sensor 2 is disposed between at least two mounting parts 4, 4. Then, by a sensor operating means 3, a countable output signal is generated and fed to the force sensor 2 on the basis of a change in a force generated due to a change in the radium of curvature of the tire tread in a grounding part due to the rotation of a tire. At this time, when the force sensor 2 is attached to the rigid base body 1, it can be installed firmly by a simple operation. As a result, even when the tire is turned at high speed, fear that the malfunction, the failure or the like of the force detecting sensor 2 is generated can be reduced, and the rotational speed of the tire can be counted with good accuracy. In addition, the rotational speed of the tire being rotated can be counted in real time by the sensor operating means 3, and the usage state of the tire can be monitored quickly and properly even while the car is traveling.