Current breaker, safety circuit and secondary battery pack

A current cut-off device comprising:

• a plate-shaped terminal piece having a contact;
• a movable piece including an elastic portion formed in a plate shape so as to be elastically deformed and a movable contact arranged at one end portion of the elastic portion and having the movable contact so as to be pressed against and in contact with the contact;
• and
• a thermally actuated element which biases the movable piece by deforming in accordance with a temperature change and causes a state of the movable piece to be shifted from a conductive state in which the movable contact is in contact with the contact to a cut-off state in which the movable contact is separated from the contact, wherein
• an end portion of the movable contact and an end portion of the contact overlap,
• when the state of the movable piece is shifted from the conductive state to the cut-off state, as the movable contact moves, it snaps and moves above the contact so that positional relationship between the end portions of the movable contact and the contact switches, and
• a direction in which the movable piece presses the movable contact to the contact and a direction in which the thermally actuated element biases the movable piece match.