PURPOSE: To simplify a circuit constitution by executing count control processing with the arithmetic processing in the unit of words not attended with the bit shift arithmetic processing.

CONSTITUTION: A random/inverse random processing means 1 inverts and outputs the bits of an output data to a MODEM 5 when a bit inverse flag data is a prescribed value such as 'true'. A count control processing means 3 sets the content of a numeral to an initial value when all prescribed bits of a data representing the result of shift calculation are not coincident with bits inputted next to a bit shift arithmetic means 4 or the value of a bit inverse flag data is true. Thus, random code processing or decoding is executed with a simple circuit by the execution of the arithmetic processing in the unit of words not attended with the bit shift arithmetic processing and the consecutive production of the code with a short period generated not applied with random processing on the property of the generation polynomial is prevented.