To achieve an additional function of thermal protection using simple components and construction.

A protection circuit of a battery for a battery pack provides a thermal sensor 12 and control circuits 8 to 11. The protection circuit connects a secondary battery 1 and control switch elements for charge and discharge Q1, Q2 in series. The protection circuit determines over-charge and over- discharge based on a battery voltage and controls to turn the control switch elements Q1, Q2 off. The thermal sensor 12 detects a temperature of the battery pack. When the control circuits 8 to 11 determine that the temperature of the battery pack rises abnormally based on a signal from the thermal sensor 12, the control circuits 8 to 11 control to turn the elements Q1, Q2 off. When the protection circuit determines that the temperature of the battery pack rises abnormally, the protection circuit turns the elements Q1, Q2 off to stop to charge or discharge. The protection circuit can place a function of thermal protection in an IC and protect against temperature using few external components.