An environment control system includes: a control unit; a serial communication bus including a main communication line having a first end connected to the control unit and first to Nth (N: an integer of 2 or more) sub communication lines branched off from a second end of the main communication line; devices connected to the first to Nth sub communication lines; and switching units disposed on all the first to Nth sub communication lines and configured to connect and disconnect the devices to and from the control unit. Each of the first to Nth sub communication lines is connected to one or more of the devices.