PURPOSE: To attain compensation due to external disturbance by using a signal of normal-reverse or reverse-normal as "1" data in a signal of normal-reverse- normal and using a signal of normal-reverse-reverse or reverse-normal-normal as "0" data in a signal of normal reverse-veverse-normal to transmit/receive data thereby attaining data check without adding a data for check.

CONSTITUTION: The signal of normal-reverse is used as "1" data in the signal of normal-reverse-normal and the signal of normal-reverse-reverse is used as "0" data in the signal of normaL-reverse-reverse-normal. An example of transmission data based thereupon is shown in (a). The reception side receives sometimes a signal of normal-reverse-reverse-reverse-normal as shown in (b) not in matching with the basic waveform due to the effect of external disturbance. Further, a signal of normal-reverse-normal-normal-reverse-reverse-normal as shown in (c) is received. The condition where a signal with ≤3 consecutive reverse level after a normal level and a signal with ≤2 consecutive normal levels after a low level cannot be received as ineffective data respectively is preset in the reception side. Thus, signals shown in (b) and (c) are not received as the data.