PURPOSE: To preclude unnecessary power consumption by judging that a stationary body is positioned when the generated voltage of a piezoelectric body is higher or lower than a reference voltage within a specific time or that a moving body is positioned when the voltage becomes a high and a low voltage.

CONSTITUTION: When the moving body moves on an electric carpet, the application state of the piezoelectric body 1 changes and the generated voltage varies. The generated voltage of this piezoelectric body 1 is passed through the LPF consisting of resistances 7W9 and capacitors 10 and 11 to remove noises generated under the influence of a power source frequency, and the voltage is amplified 12; and its DC component is cut off 13 and the signal is inverted in phase and amplified by an amplification factor set by a variable resistance 16. Then when the input from an amplifier 15 is lower than a set value of 3V, a 0.3sec delay time after, the input to a microcomputer 19 from the amplifier 15 rises above a set value of 7V, the microcomputer 19 judges that there is the moving body on the electric carpet and energizes the electric carpet with its output. Further, when the stationary body is placed on the electric carpet and when the voltage is higher than the 1st set value of 7V or lower than the 2nd set value of 3V, the electric carpet is not energized.