A breaker, comprising: a first stationary contact, comprising a first stationary contact portion; a movable contact, comprising a first movable contact portion; an actuating member, connected to the movable contact to actuate the movable contact to move in a first direction between an open position and a closed position, at the open position, the first movable contact portion being spaced apart from the first stationary contact portion, at the closed portion, the first movable contact portion being in contact with the first stationary contact portion; a first arc extinguishing device, comprising a plurality of arc extinguishing grid sheets; a first arc running piece, extending from a first arc running end portion of the first arc running piece arranged adjacent to the first stationary contact portion to a second arc running end portion of the first arc running piece, to guide an electric arc from the first stationary contact to the first arc extinguishing device; and an arc guiding piece comprising a first arc guiding section extending in the first direction, the first arc guiding section being arranged between the movable contact and the first arc extinguishing device in a second direction perpendicular to the first direction, to guide an electric arc from the movable contact to the first arc extinguishing device, wherein the second arc running end portion of the first arc running piece and the first arc guiding section are arranged at opposite sides of the first arc extinguishing device in the second direction, the first arc running piece passes through the plurality of arc extinguishing grid sheets of the first arc extinguishing device, characterized in that in the second direction, a shortest distance between the movable contact and the first arc guiding section is approximately equal to a shortest distance between the first arc guiding section and the arc extinguishing grid sheets, and the first movable contact portion is a flat surface; upon the movable contact being at the open position, the first movable contact portion is closer to the first stationary contact than the arc guiding piece in the first direction, and upon the movable contact being at the open position, a shortest distance between the first movable contact portion and the arc guiding piece in the first direction is approximately equal to a shortest distance between the movable contact and the first arc guiding section in the second direction. a first stationary contact, comprising a first stationary contact portion; a movable contact, comprising a first movable contact portion; an actuating member, connected to the movable contact to actuate the movable contact to move in a first direction between an open position and a closed position, at the open position, the first movable contact portion being spaced apart from the first stationary contact portion, at the closed portion, the first movable contact portion being in contact with the first stationary contact portion; a first arc extinguishing device, comprising a plurality of arc extinguishing grid sheets; a first arc running piece, extending from a first arc running end portion of the first arc running piece arranged adjacent to the first stationary contact portion to a second arc running end portion of the first arc running piece, to guide an electric arc from the first stationary contact to the first arc extinguishing device; and an arc guiding piece comprising a first arc guiding section extending in the first direction, the first arc guiding section being arranged between the movable contact and the first arc extinguishing device in a second direction perpendicular to the first direction, to guide an electric arc from the movable contact to the first arc extinguishing device, wherein the second arc running end portion of the first arc running piece and the first arc guiding section are arranged at opposite sides of the first arc extinguishing device in the second direction, the first arc running piece passes through the plurality of arc extinguishing grid sheets of the first arc extinguishing device, characterized in that in the second direction, a shortest distance between the movable contact and the first arc guiding section is approximately equal to a shortest distance between the first arc guiding section and the arc extinguishing grid sheets, and the first movable contact portion is a flat surface; upon the movable contact being at the open position, the first movable contact portion is closer to the first stationary contact than the arc guiding piece in the first direction, and upon the movable contact being at the open position, a shortest distance between the first movable contact portion and the arc guiding piece in the first direction is approximately equal to a shortest distance between the movable contact and the first arc guiding section in the second direction.