With the aim of offering a video display technique by which stable and high contrast video images are reproduced, contrast adjusting circuitry is constructed. The lever member includes a rod to be inserted into the knob and a lever base having an end face to which the rod is connected. The upper and lower heat exchange tubes are connected by a plurality of vertical heat tubes. The MI sensor element 1 outputs a voltage corresponding to a magnetic field strength acting on the magneto-sensitive bodies 2 from the detecting coil 3 by flowing a pulse current or a high-frequency current to the magneto-sensitive body 2. Upper fastening portions provided at front ends of seat rails constituting part of the rear sub-assembly are fastened to mounting holes formed in the brackets. In the low power mode, the output voltage is equivalent to the input voltage.