A power conditioner is provided that includes a heat dissipating member, multiple circuit boards, and a mounting auxiliary plate. A power conditioner circuit including an electric heat generating element is formed on each of the circuit boards. The circuit boards are mounted on a front surface of the heat dissipating member. Heat dissipating fins are arranged on a back surface of the heat dissipating member. Preferably, the heat dissipating member is formed from a material having high heat dissipation property. The mounting auxiliary plate is fixed to the back surface side of the heat dissipating member and provided with a through hole for mounting to a wall. The mounting auxiliary plate has higher rigidity than the heat dissipating member.