An eraser of a blackboard is provided to make a semiautomatic structure without manually exchanging the left and right sides of an eraser frame by forming a butt plate. In the eraser of a blackboard, a combined body is formed by attaching an attachment face(12) to a bottom side(6) of an operating plate with an adhesive agent, applying the adhesive agent on a bottom side(82) of an adhesive cloth(81), and then attaching a fiber fabric cloth(86). An adhesive surface(84) of the combined body is detachable from the adhesive surface of the attachment face. A cut face(78) is formed by digging left and right sides(74) of an erase frame(71) in the predetermined depth. A combined body is formed by attaching the bottom sides of adhesive cloths(93) on the cut face by applying the adhesive agent and attaching bottom sides(99) of two fiber fabric cloths(98) by spreading the adhesive agent on each bottom side of two fiber fabric cloths. Two adhesive surfaces(96) are detachable from the cut faces of the left and right sides. A butt plate(8) is joined to the left side of an upper reciprocating plate. An operating pin is formed as a single body.
