PROBLEM TO BE SOLVED: To make a terminal equipment light, eliminate a fear that data are stolen or that a CPU is becoming old-fashioned, to save a trouble such as the install work of an application or the like or data maintenance, and to simply and highly efficiently compress data. SOLUTION: This data transmitting and receiving device transmits the data of a screen to a terminal equipment by radio or by wire. Then, the data of the screen are transmitted to the terminal equipment as bit map data constituting the screen, and screen display is operated. At that time, the bit map data are divided into blocks, the number of indexes for displaying each picture element is reduced according to the number of colors to be used in each block is small, and the data are converted into the index with the further small number of bits, compressed, and transmitted. Also, the blocks are defined as the units of the number of 10K-50K picture elements. Moreover, this device is provided with a changed rectangle detecting means 12 which detects only a part changed compared with the previous screen in the data constituting one screen, and the changed rectangle is detected, and the data of the changed rectangle part are transmitted.
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