PURPOSE: To enable the measurement of wavelength covering the region from microwave to an infrared by arranging a structure suitable for ultraminiature designing with excellent weather resistance property.

CONSTITUTION: Electrons are released from an electron releasing section comprising a cold cathode 1 and a gate electrode 2 are released and turned by an orthogonal magnetic field by a magnetic field application means 4 being introduced to the side of an anode 3 by an electric field E to increase the stoke length of a moving locus while the electrons are accelerated by a cyclotron resonance as generated when a value of cyclotron angular frequency ωc determined by a flux density of the orthogonal magnetic field coincides with a value of an angular frequency ωf of an incoming electromagnetic wave so that the electrons accelerated impinge molecules M of a diluted as to ionize. As a result, ion pairs are multiplied to be trapped with the anode and the cathode. A cyclotron resonance is caused by varying the flux density and here, a peak point is observed in an anode current thereby enabling the detection of the length of the electromagnetic wave corresponding to the angular frequency ωc.