An image display device has a serial port as data input and output port for the system, and input and output data converting element for mutually converting the data format of input and output data for wireless communication. A data processing device has input and output processing virtual element for processing data input and output virtually as if the data input and output port are connected directly. The input data of the serial port is converted by the input and output converting element, and is transmitted to the data processing device through a wireless unit, and is processed through the input and output processing virtual element. The output data of the data processing device is transmitted to the image display device in the wireless unit by way of the input and output processing virtual element, and is converted by the input and output data converting element, and is issued to the serial port. At this time, depending on whether the serial port is being used or not, the control level of power saving operation is changed. In this configuration, the input and output peripheral device can be used at the display side, and power saving control in harmony between display function and input and output peripheral device function is realized.