To provide an encoder and a decoder which improve an error propagation suppression and ECC correction ability while avoiding increase in circuit size.

The encoder includes a means for branching an RLL code into a restraining part corresponding to a basic code and a non-restraining part corresponding to an information bit itself, a first encoder means for adding an error correction code to the restraining part for RLL encoding, a second encoder means for adding an error correction code to the non-restraining part, and an interleave means for interleaving outputs of the first and second encoder means to output encoded information.