To evade influence by electromagnetic noise by transmitting and receiving the same signal by using two kinds of different frequency bands in a radio LAN system regarding an electromagnetically compatible(EMC) communication system.

A cable LAN system 23 is constructed in a module body 80 of a space station and personal computers PC-1 to PC-3 are connected to the system 23. An access point 21 with an antenna 21A is connected with the cable LAN system 23, a notebook computer 6A is equipped with two integrated type radio LAN cards 1, a notebook computer 2B is equipped with LAN cards 2 each having a separation type antenna 2B and the same information is simultaneously transmitted and received by a radio wave by using the frequency bands of 2.4 GHz, 19 GHz by each of two cards. Since communication with a system 30 is performed by the radio waves of two kinds of different frequency bands via the access point 21, when one frequency band is influenced by the electromagnetic noise, a signal in a normal frequency band is used during the period and therefore, accurate communication is performed without being influenced by electromagnetic waves.