To provide an encoding and synchronizing method capable of attaching a synchronized signal (flag) to each of the prescribed number of transmission information bits to perform transmission with a simple method and transmitting the synchronized signal to a receiver.

In this method for encoding and synchronizing an orthogonal multi-carrier signal by an orthogonal frequency division multiple signal system, an encoding part sends a synchronous flag signal synchronized with the transmission information bits to an OFDM transmitting part in each of the prescribed number of transmission information bits, and the OFDM transmitting part performs OFDM modulation of transmission information on the basis of the synchronous flag signal, attaches a transmission number to the transmission information in each of the prescribed number of transmission information bits and respectively transmits the transmission number as a synchronous flag by using a specified carrier.