In a normal operation state, a connection management section writes data transmitted from a first processing section to a data temporary storage section and reads data to be received by a second processing section from the data temporary storage section. Upon receiving control signals which instruct a change of the subject of processing, the first processing section and the second processing section output a transmitting-end clear request and a receiving-end clear request, respectively. The connection management section reads data from the empty data storage section after a transmitting-end clear request is received and until a receiving-end clear request is received, and writes data to the empty data storage section after a receiving-end clear request is received and until a transmitting-end clear request is received.