PURPOSE: To realize the data compander capable of compressing/expanding data at a high speed with a small circuit scale, the image device, the electronic camera and the video telephone system.

CONSTITUTION: The data compander consists of a serial circuit having a redundancy section not used at compression but used at expansion so as to attain inverse conversion with the same circuit configuration, of a data conversion arithmetic unit 54 applying linear DCT(discrete cosine transformation) and inverse DCT operations to output data from a parallel-serial converter 11 in the case of compression through bus changeover respectively in a form of serial arithmetic operation and of a controller 55 providing a control signal to each section to control the entire operation and outputting a bus switching signal to the data conversion arithmetic unit 54 to control the switching of the connection state of each block. The controller 55 outputs a bus switching signal to the data conversion arithmetic unit 54 in the case of expansion to switch the connection state of each block of the data conversion arithmetic unit 54 and executes the data conversion arithmetic operation and the inverse conversion arithmetic operation with the same circuit configuration.