To provide a serial communication method and a bidirectional real communication system, wherein malfunctions are prevented while a speed is increased in a simple configuration.

The bidirectional serial communication system has a first module, a second module and a trunk bus to which the first module and the second module are connected. The first and second modules have a transmission part and a reception part, respectively. The transmission part has preamble at the leading part of transmission data, inserts a frame end signal to the end of the transmission data and turns a signal transmission line to a high impedance state. A reception part detects the end signal and stops the reception operation of a reception circuit for a fixed period or invalidates reception data.