To provide a highly reliable protection element for a storage battery.

The protection element 201 is constituted of a low-melting-point metal body 207 and heating elements 203 and 205. The low-melting-point metal body 207 is connected to a charger side line 51 and a storage battery side line 53 of a charge/discharge circuit. The heating element 203 is connected to the storage battery side line and a switch 255, and the heating element 205 is connected to the charger side line and a switch 253. When the switches are operated, a voltage not influenced by a voltage drop of the low-melting-point metal body is applied to either of the heating elements, and the low-melting-point metal body can be surely blown out.