A forward error correcting transmitter and receiver for preventing the erroneous detection of synchronization is provided in a system in which synchronization of an interleaver circuit and a deinterleaver circuit, to be inserted between a convolutional encoder and a Viterbi decoder, is obtained from a synchronization detecting circuit of the Viterbi decoder. A LFSR (Linear Feedback Shift Register) is used as a row-direction address counter during writing and an up/down counter is used as a column-direction address counter during reading, during the interleaver circuit. In the deinterleaver circuit, an up/down counter is used as the column-direction address counter during writing, and an LFSR is used as the row-direction address counter during reading.