PURPOSE: To always accurately carry out the measurement and display of the pressure of a tire by providing an energy transmitting device fitted to the chassis of a vehicle, an energy transfer device fitted to the wheel thereof, and a tire-pressure signal generating device or the like respectively.

CONSTITUTION: When an ignition switch 7 of a vehicle is closed, a current is supplied to a power transmitter 8 from a generator 6. Then, a primary coil 9 fitted to the chassis of the vehicle transmits a prescribed frequency to a tuning circuit 10 fitted to the wheel of the vehicle. A transducer 1 supplied with power from the tuning circuit 10 is compressed up to a prescribed pressure, when it is supplied with power from the tuning circuit 10, to close the open end of the chamber. Further, the output of the transducer 1 is supplied to a signal regulating circuit 2 as a voltage. On the other hand, the change in the consumption of the primary power is detected by a detector 3 connected to the primary coil 9. After converted into pressure information by a processor 4, the detected result is output to a display 5.