A Reed Solomon decoder which can perform high-speed decoding operation without significantly increasing the circuit scale. The Reed Solomon decoder includes the following: input parameter operator 309 which generates syndrome and erasure data for a data sequence, decoding operation processing unit 304 which performs the decoding operation using the aforementioned syndrome and erasure data based on the command code indicating the prescribed decoding operation, and which generates the error data and error position data, and correction operation executor 312 which performs the correction operation using the aforementioned error data and error position data. The decoding operation processing unit 304 has an multiplier and an adder which execute the product and sum operation of the Galois field in one step.