To provide a transmission/reception method which is strong against external noise environment by utilizing a signal infrared-ray wavelength, that is a single infrared-ray diode, and transmitting and receiving transfer data in parallel.

Serial data to be transmitted are converted into parallel data through a serial/parallel converter 21, and a PN code provided with mutual orthogonality generated by the input of clock signals in a PN code generation part 25 is multiplied with the respective parallel data in multipliers 220-22n. Then, the output data of the multipliers 220-22n are totaled as a single signal in a totaling device 23 and outputted as an infrared-ray signal through a single infrared ray data output part 24. In the meantime, on a receiver side, the PN code generating part for generating and outputting the same code as a transmitter side is provided, the PN code outputted from there is multiplied by the one for which infrared-ray data are converted into electric code signals and reception signals are attained.