A receiver for generating a transmission symbol stream by applying predetermined modulation processing to an encoded bit series obtained by encoding an information bit series having a predetermined transmission rate. The receiver generates a transmission-information bit series having a transmission rate lower than a predetermined transmission rate in accordance with an information bit series and receives a transmission signal generated in accordance with the transmission-information bit series through a communication channel. The receiver stepwise increases the low transmission rate of the transmission-information bit series to reach a predetermined transmission rate by stepwise increasing the low transmission rate, while stepwise increasing the number of communication channels to be used in accordance with the stepwise increase of the low transmission rate.