A power supply apparatus is equipped an assembled battery, a case that accommodates the assembled battery, and a connecting mechanism that is attached to an outside of the case, wherein the connecting mechanism connects two selected cells. The connecting mechanism includes a fixation portion and a disconnection portion. The fixation portion includes a first conductive plate that is directly connected to a positive electrode terminal of one of the two selected cells, and a second conductive plate that is directly connected to a negative electrode terminal of the other of the two selected cells, wherein the fixation portion is attached to the case. The disconnection portion is removable from the fixation portion, electrically connects the first conductive plate to the second conductive plate when attached to the fixation portion, and electrically disconnects the first conductive plate from the second conductive plate when removed from the fixation portion.