In a digital TV broadcast signal receiver connected to a multi-directional antenna called smart antenna, when a TV broadcast signal of an optional channel becomes unreceivable for any reason, it makes possible to restart displaying an image on a screen of a monitor display device, quickly. The host computer includes a displacement acquiring unit for acquiring a displacement of the moving mechanism and a measurement value calculating unit for calculating a measurement value. The output circuit is so set that the driving force during the second half of signal transition is lower than the driving force during the first half of transition. The client devices receive transmissions from other client devices serviced by the plurality of access points and characterize the received transmissions to determine signal qualities of the plurality of transmissions received from the other client devices.