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
• when the state of the movable piece is shifted from the conductive state to the cut-off state, as the movable contact moves, the movable contact gets over the contact, 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.