A system management bus (SM Bus) system includes an arbitrator; a slave device connected to the arbitrator via an SM Bus; a first master device connected to the arbitrator capable of sending a first start command for communicating with the slave device; and a second master device connected to the arbitrator capable of sending a second start command for communicating with the slave device. The arbitrator set the first master device to have a priority, and when the first start command is being executed and the arbitrator receives the second start command, the arbitrator confirms whether the SM Bus is busy or not after a second predetermined time, and if the SM Bus is not busy, the arbitrator transmits the second start command to the slave devices via the SM Bus.