An optical information medium includes a disk-shaped substrate having a center hole, an annular information recording area thereon, and an annular resin-based light-transmitting layer thereon by which recordingreading laser beam is transmitted to the information recording area. Thus, the frequency of input of an image signal to each pixel of the liquid crystal display device can be increased. A control signal is generated to control a synchronous rectification transistor in response to an on-time of a switching signal, a level of a transformer voltage and an output voltage of the power converter.