Abstract: A data transmitter/receiver apparatus transmits host computer screen data by wireless interface or by cable to terminal. Also, the screen data is transmitted to the terminal as the bit-mapped data constituting that screen, and screen display is performed. At that time, the bit-mapped data is divided into blocks, converted into indexes having a smaller number of bits than the pixels to transmit, making the number of bits in the indexes representing each block of pixels smaller as the number of colors used within each block is smaller, and compressed before sending; the blocks may be made in units of 10K-50K pixels. Furthermore, only the parts changed in the data composing one screen are detected by comparing with the screen one screen before, and transmits the data of the changed rectangular portion when the changed rectangle detector has detected as a changed rectangle the region computed by .vertline.X1-X2.vertline..times..vertline.Y1-Y2.vertline.