An automatic transmission control unit determines whether or not a constantly open failure, in which a switch valve cannot switch a pressure regulating valve and a second hydraulic chamber to a non-communicative state, has occurred on the basis of a parameter representing a dynamic characteristic during a shift from a first gear position to a second gear position. Thus, the contrast is controlled according to the brightness mean of one of the video signal having the controlled contrast and the video signal having the increased middle brightness signal level, which enables displaying an optimal image. The processing unit may be configured to transmit the processed signal to a controlled device that is configured to receive the processed signal.