To provide a battery pack for an electric vehicle capable of enhancing the strength of the entire side wall of a tray, a battery pack for an electric vehicle includes: a tray 3; and at least one outer frame 6 disposed on an outer side of a side wall surface of the tray 3, the outer frame 6 extending along the side wall surface and being welded thereto so as to cover the side wall surface. The cup holder further includes a hollow case that is mounted behind each mounting hole of the holder base, a support member inserted into the hollow case, and a return spring positioned between the support member and the hollow case. The optical probe is capable of measuring the velocity of particles in a gas flowing through the internal bore. The cap has an aperture cut into it through which the cable passes therethrough. Then, the organic insulating film is etched using the silylated layer as a mask, thereby forming an opening, which will be a via hole or interconnection groove, in the organic insulating film.