A separate operational section for determining the degree of a polynomial is provided to increase the process speed in determining both error locator and evaluator polynomials. When a received word is decoded based on the error location found, the received word is stored in a memory and corrected and output through the designation of the address. The formula (t - 1) is derived from the error locator equation and the value of which satisfies ?(.alpha.) = O is determined to increase the process speed. The decoder and the encoder share part of the hardware to make the system compact.
