This signal detection method detects an output signal indicating data information contained at least in two sideband waves from an input signal having a carrier and at least two sideband waves accompanying the carrier. The method includes a cut off step (32) for cutting off a sideband wave positioned at the high frequency side or the low frequency side as compared to the carrier from the at least two sideband waves and a square detection step (33) for outputting an output signal by performing square detection of an input signal having one of the sideband waves which has been cut off.