This International Standard describes the measuring method for the level of intermodulation products generated in a gyromagnetic device. When two or more signals of different frequencies enter into a device and/or equipment having non-linear characteristics (contact point, flexible waveguide, ferrite device, etc.), harmonics are generated in that device and/or equipment. Moreover, differential or added frequencies occur in the device due to mixing of harmonics or a harmonic and the fundamental frequency. These resultant frequencies create noise causing interference. In transmitter/receiver duplexing systems and radio relay systems, many frequencies are allocated to a specified band so that combinations of transmitting frequencies and harmonics may fall on the receiving band. This causes deterioration of communication quality due to intermodulation. Since the intermodulation interferences cannot be prevented by filtering, it is important to evaluate the intermodulation products level of the device to be employed in such a system.