A multiplexing communication system is capable of maintaining an appropriate response speed of a control with respect to an electromagnetic motor based on an encoder signal during multiplexing and transmission of the encoder signal. A transmission data composition processing section of a multiplex communication device multiplexes encoder signals ENCD1 to ENCD8 output from a linear scale and a rotary encoder into frame data FRMD and transmits the data. The transmission data composition processing section sets the encoder signals ENCD1 to ENCD8 to bit positions of the frame data FRMD respectively corresponding to the linear scale and the rotary encoder. At the bit positions where the encoder signals ENCD1 to ENCD8 are set, the encoder signal ENCD and information showing the presence or absence of the data of the encoder signal ENCD are alternately set for each cycle of transmission of the frame data FRMD.