To improve the operability of an equipment by giving the equipment a stable inclination when a main body of the equipment is installed, due to the cooperation between an AC adaptor and a cover which is rotatably installed on the AC adaptor in the case that the AC adaptor is installed on a bottom face of the main body of the equipment.

This AC adaptor has such a structure that a battery pack can be mounted and demounted in a power supply installing section 12 which is installed on a bottom face of a main body 1A of an equipment and part of it may project on the bottom face of the main body when another part is installed in the power supply installing section 12. The AC adaptor 2 has a main body 2A, a cover 3 which is rotatably installed on the main body of the adaptor, and a projection 2B which is integrally formed with the main body of the adaptor and which can be set in the power supply installing section. When the projection 2B is installed in the power supply installing section with the cover 3 being opened at 180° from the main body of the adaptor, the height of an external face of the cover is the same as that of an external face of the AC adaptor and so the adaptor can be installed, the projecting state under the main body of the equipment.