To detect an abnormal temperature adequately by reducing heat transfer loss and also to reduce the cost by reducing the number of temperature sensor units and the manhour for installation.

In a set battery 1, a plurality of unit batteries 2 in a rectangular parallelopiped type which are constituted by arranging a plurality of single batteries 3 are arranged in parallel in the direction rectangular to the arrangement direction of the single batteries 3. A temperature sensor unit 5 constituted by connecting a necessary number of temperature sensors 6 at suitable intervals is arranged between the unit batteries 2, 2, and made to reciprocate at least one time along the single battery arrangement direction of the unit batteries 2. As a result, the number of the temperature sensor units 5 is made smaller than at least one-half of the number of each of the unit batteries 2. By detecting a temperature on the side surface of each of the single batteries 3, the heat transfer distance from a pole plate group of the single batteries 3 is made minimum, and heat transfer loss is reduced.