A database stores map data including road network data and landmark data. The latch mechanism includes a holding frame and a latch, the holding frame being affixed with one of the shell body and the platform, and the latch being assembled with the other one of the shell body and the platform. Because the center tine is about twice the width of the left and right tines, two pallets, side-by-side, can be carried simultaneously with only three tines. The arcuate portion is further capable of the rocking act to cause the backrest to revert to the previous upright position relative to the floor surface. Still, the invention may be further used to treat virus-diseases such as Hepatitis B, Hepatitis C, AIDS and etc. In this way, in x-ray exposure, blur caused by secondary electrons is suppressed using a wavelength region of relatively shorter wavelengths.