PURPOSE: To enable easy changing of an installing place, by a method wherein a power surce part, an oscillating circuit, a resonating circuit, and a detecting circuit are housed in a single receptacle, and are secured to the receptacle in a manner to electrically connect a conductive rod, forming a detecting line, to the resonating circuit and detecting circuit.

CONSTITUTION: In a receptacle 5, a portable power source part 6 such as battery power source, a high-frequency oscillating circuit 7, a resonating circuit 8 which has a resonating frequency of f0 and boosts an amplitude to 10W20 times, a conductor rod 9 connected to the output of the circuit 8 and a detecting circuit 10, and a display meter M for displaying a detecting state by means of the output of the detector 10. If a human body approaches the conductor rod 9, an electrostatic capacity C0 between the rod 9 and an earth changes slightly, and an amplitude of a frequency signal f0 applied to the rod 9 fluctuates according to the change in the capacity. Only a frequency f1, being produced when the human body approaches and being within the fluctuations in the amplitude of the frequency signal f0, is detected by the circuit to perceive approaching of the human body.