In the case where two wireless communication systems are located close to each other and possibly interfere with each other, it is detected if broad band interference takes place, and, when broad band interference takes place, the use of frequencies is limited within such a frequency range in which the wireless communication systems are little affected by the interference. An interference detection system for detecting interference between one system and another system in a wireless communication making use of frequency division multiplexing is described. The interference detection system includes a radio frequency signal receiving unit; a signal level storing unit; a calculation result storing unit; a threshold level comparing unit; and a carrier number storing unit.