BREAKER, AND SAFETY CIRCUIT AND SECONDARY BATTERY HAVING THE SAME

PROBLEM TO BE SOLVED: To miniaturize a breaker used as a protective device of a secondary battery or the like without filling failure of resin material and strength degradation of a resin case.SOLUTION: A breaker includes: a fixed piece 2 which has a fixed contact; a movable piece which has a movable contact at its tip and presses the movable contact to the fixed contact to bring them into contact with each other; a thermally-actuated element which actuates the movable piece so that the movable contact is separated from the fixed contact by deformation according to temperature change; and a case body 71 of a resin case which accommodates the fixed piece 2, the movable piece and the thermally-actuated element. The case body 71 includes recessed parts 75, 77 depressed from a peripheral part. The fixed piece includes a retreat part 25 which retreats with more than a predetermined first distance D1 from the recessed parts 75, 77 of the case body 71 and is embedded in the case body 71.