PURPOSE: To enlarge a cost merit and a space merit by sharing a divider at the time of transmitting and receiving data.

CONSTITUTION: At the time of transmission, an input selection means 1 selects transmission data Ds and inputs it to the divider 2. An output selection means 5 selects a code addition circuit 3 and outputs data obtained by adding a CRC code to transmission data Ds. At the time of reception, reception data Dr is selected in an input selection means 1 and is inputted to the divider 2. The output data selection means 5 selects an error check circuit 4 and outputs a check result. Division required for the detection of a CRC error can be executed by sharing one divider at the time of adding the CRC code and at the time of checking. Thus, the cost merit and the space merit can be enlarged.