A portable computer includes a portable computer body having an upper surface, a lower surface and a lower front edge thereof. An add-on battery is detachable mounted on the lower surface of the portable computer body and has a wedge-shaped portion corresponding to a wedge-like space which is defined between the lower surface of the portable computer body and a surface on which the portable computer body is placed, when the portable computer body is placed to be inclined about the lower front edge of the portable computer body. The portable computer body is, when it is equipped with the add-on battery, inclined in such a manner that the upper surface of the portable computer body is lower at a front edge thereof.