In order to reduce the crest factor of a signal for power amplification, a windowing function is applied. The picture frames are combined to produce a number of pairs of frames which constitute a stereoscopic image of the target area. A door glass, a sliding roof or the like then reciprocate slightly via a window regulator driving circuit, a sun roof driving circuit or the like. The peripheral device detects the signal as being present and begins measuring a time period with the AM receiver.