To provide a miniaturized battery that has a built-in safety device accurate in sensing an abnormality, having a self-holding property and suppressed in functional deterioration even if used in an electrolyte.

A safety device 6 built in an outer can 2 of the safety device built-in battery 1 includes a current supply side terminal, a movable arm, a current output side terminal, bimetal and PTC, and is disposed in a resin case. When the battery is normal, a current flows through the current supply side terminal, the movable arm and the current output side terminal to bypass the bimetal and PTC. Upon an abnormality, the bimetal is inverted so that the disconnection of the movable arm from the current output side terminal disables the current to flow through the current supply side terminal, the movable arm and the current output side terminal, and that the connection of the current supply side terminal, the movable arm, the bimetal and the PTC causes the PTC to generate heat, thus keeping the disconnection of the movable arm from the current output side terminal.