PURPOSE: To demodulate a modulation signal even when amplification factor is not determined at optimum, in a pulse width modulation receiving device, and the pulse widths of the transmitted pulse width modulation signal and the demodulated pulse width modulation signal are not coincident to each other.

CONSTITUTION: The change point of pulse width of repeatedly received pulse width modulation signals is detected by a pulse width detecting means 11a, and the detected number is added to a pulse width memory means 11c corresponding to the sampling address of the detected timing. A sampling trigger forming means stochastically judges the change point of pulse width from the detected number of each address of the pulse width memory means 11c, and determines the trigger timing of sampling trigger signal, and thereafter, a sampling decoding means 7 demodulates the pulse width modulation signal according to the sampling trigger signal. Thus, even when the amplification factor of a pulse width modulation receiving device is not necessarily optimum, decode can be performed. It is not required to necessarily determine the optimum amplification factor, and an amplification factor determining circuit can be simplified.