Intended is to achieve, in a wide range of an SN ratio, throughput on the same order of that attained by a method based on puncturing and improve computational complexity of decoding processing at a high coding rate. In a communication system for transmitting an error correcting code for an error on a communication path from a transmitter to a receiver, the transmitter divides information bits of a code word to be transmitted into a plurality of blocks based on a request for retransmission of an error correcting code from the receiver, generates an error correcting code by compact-coding of one block among the plurality of blocks and transmits the generated error correcting code.