NOVELTY - The breaker (1) has a movable piece (4) for pressing a movable contact to a stationary contact. A thermal-actuation element (5) operates the movable piece such that the movable contact is separated from the stationary contact by deformation in connection with temperature change. A fixed piece, the movable piece and the thermal-actuation element are accommodated in a case. The movable piece is provided with a contact part (42) that is contacted in the case. A clearance gap is formed between the contact part and the case and filled with filler i.e. resin (74h).    USE - Breaker for use as a protection apparatus in an electric equipment safety circuit, a secondary battery circuit (all claimed) and an electric equipment secondary battery pack of an electric appliance, a motor vehicle and a domestic electrical appliance.    ADVANTAGE - The air tightness between the movable piece and the case is improved by filling the filler in the clearance gap between the contact part and the case, so that bond strength of an area from the movable piece to the case can be raised, extremely high sealing performance can be acquired, moisture content and flux penetrates into an inner side of the case can be prevented by improving sealing property of the case, generation of rust in metal parts can be prevented, the filler flows into an interior space can be prevented, normal heat deformation operation of the thermal-actuation element can be maintained and favorable temperature characteristic can be acquired. The simplification of a manufacturing process of the breaker is achieved, so that productive efficiency can be improved. The normal operation of the thermal-actuation element inhibited with respect to the filler can be prevented. The safety of a safety circuit or a secondary battery pack can be ensured.    DESCRIPTION OF DRAWING(S) - The drawing shows sectional views of a resin material filled in a case, which is sealed.    Breaker (1)    Movable piece (4)    Thermal-actuation element (5)    Contact part (42)    Resin (74h)