According to one embodiment, in a double-ring network, a master station includes a transmitting and receiving permission switch portion, a communication port A at an A-system side, a communication port B at a B-system side, a first receiving control circuit portion, a transmitting and receiving control circuit portion, a frame detection determining circuit portion, a frame data generating circuit portion, a logical address determining circuit portion, a live list setting circuit portion and an address list setting circuit portion. The master station determines a token order (a transmission priority, also called a logical address) using a shortest path function by the logical address determining circuit portion and the address list setting circuit portion such that the token order does not depend on physical addresses of transmission stations and is matched to a connection order of transmission stations to realize path optimization. This reduces a transmission time.