Between a CPU and a communication module, a write buffer, a write control section, a read buffer and a read control section are provided. The CPU directly accesses and the write buffer and the read buffer. By periodically outputting a communication request, the read control section reads data, which the communication module received from other nodes, and transfers the data to the read buffer. The write control section transfers to the communication module the data written in the write buffer as transmission data. In addition, a bypass access control section and an access sequence control section are provided. The bypass access control section controls direct data read and data write between the CPU and the communication module. The access sequence control section controls sequence of accesses of the control sections to the communication module.