To secure operating characteristics of a temperature fuse and to improve reliability by realizing miniaturization and compactness of a protection device obtained by unitizing a temperature fuse protection component to a mounting substrate of a protection circuit.

The protection device is made as small and thin as possible by unitizing the protection circuit including control elements 36, 37 incorporated into the mounting substrate 35 to the protection component of the temperature fuse 10 in which a fusible body fuse element of a low melting point alloy arranged on one surface of a ceramic substrate is sealed by a ceramic cap, and in which a lead member and a resistor heating element are arranged on the other surface. Here, the temperature fuse protection component is mounted so that a cap side is fitted into a gap between two control elements 36, 37.