A breaker is provided with a first terminal piece on which a fixed contact is formed, a movable piece with a movable contact for pressing the movable contact against the fixed contact so as to contact therewith, a thermally-actuated element deforming with a change in temperature and moving the movable piece so that the movable contact is separated from the fixed contact, and a second terminal piece electrically connected to the movable piece. The movable contact includes a first movable contact and a second movable contact arranged at a first end portion and a second end portion, respectively, of the movable piece in its longitudinal direction. The fixed contact includes a first fixed contact arranged at a position with which the first movable contact can contact, and a second fixed contact arranged at a position with which the second movable contact can contact.