A binary code is divided into 2-bit data units. Pulse position modulation is performed on each unit rather than on each bit. Since a pulse is not formed for each bit, the transmission interval and transmission frame interval for the modulated signal is shortened, thus enabling high speed transmission. Since the pulse interval of the signal contains the information of the 2-bit data unit, only the leading edge of the pulse needs to be detected. This feature allows reliable demodulation even under adverse conditions such as a long-distance transmission route or a noisy transmission route. Since there is no need to demodulate by comparing each bit with an immediately preceding bit, complex demodulation schemes and decoding registers are not needed on the receiving side. Since the width of the pulse does not contain any transmission information, the pulse width is made as short as possible, thereby reducing battery consumption within the transmitter.