A fusion splicer comprising: a heater which heats a glass part of an optical fiber (F1, F2); a lower clamp on which a coated part of the optical fiber is placed: a coated part clamp which sandwiches the optical fiber between the coated part clamp and the lower clamp; a windproof cover which covers the heater and the coated part clamp: a retreat mechanism (30, 60) which causes the coated part clamp to retreat from the lower clamp; an opening/closing mechanism which drives the windproof cover; and a pair of glass clamps which are attached to an inner surface of the windproof cover, wherein the retreat mechanism comprises: a power source (30a, 60a); a rotating member (33b, 67a) which is rotatable around a rotation center (33c, 67c); an elastic member (32, 63) that elastically deforms by power received from the power source and thereby stores elastic energy; a transmission part (33, 67) which pushes the coated part clamp upward due to an elastic force received from the elastic member; and a restricting part (34, 68) which restricts rotation of the rotating member while the elastic member stores the elastic energy in a state in which the windproof cover is closed, and wherein the restricting part releases the elastic energy stored in the elastic member and thereby releases restriction on rotation of the rotating member in conjunction with an opening operation of the windproof cover. a heater which heats a glass part of an optical fiber (F1, F2); a lower clamp on which a coated part of the optical fiber is placed: a coated part clamp which sandwiches the optical fiber between the coated part clamp and the lower clamp; a windproof cover which covers the heater and the coated part clamp: a retreat mechanism (30, 60) which causes the coated part clamp to retreat from the lower clamp; an opening/closing mechanism which drives the windproof cover; and a pair of glass clamps which are attached to an inner surface of the windproof cover, wherein the retreat mechanism comprises: a power source (30a, 60a); a rotating member (33b, 67a) which is rotatable around a rotation center (33c, 67c); an elastic member (32, 63) that elastically deforms by power received from the power source and thereby stores elastic energy; a transmission part (33, 67) which pushes the coated part clamp upward due to an elastic force received from the elastic member; and a restricting part (34, 68) which restricts rotation of the rotating member while the elastic member stores the elastic energy in a state in which the windproof cover is closed, and wherein the restricting part releases the elastic energy stored in the elastic member and thereby releases restriction on rotation of the rotating member in conjunction with an opening operation of the windproof cover. a coated part clamp which sandwiches the optical fiber between the coated part clamp and the lower clamp; a windproof cover which covers the heater and the coated part clamp: a retreat mechanism (30, 60) which causes the coated part clamp to retreat from the lower clamp; an opening/closing mechanism which drives the windproof cover; and a pair of glass clamps which are attached to an inner surface of the windproof cover, wherein the retreat mechanism comprises: a power source (30a, 60a); a rotating member (33b, 67a) which is rotatable around a rotation center (33c, 67c); an elastic member (32, 63) that elastically deforms by power received from the power source and thereby stores elastic energy; a transmission part (33, 67) which pushes the coated part clamp upward due to an elastic force received from the elastic member; and a restricting part (34, 68) which restricts rotation of the rotating member while the elastic member stores the elastic energy in a state in which the windproof cover is closed, and wherein the restricting part releases the elastic energy stored in the elastic member and thereby releases restriction on rotation of the rotating member in conjunction with an opening operation of the windproof cover. a power source (30a, 60a); a rotating member (33b, 67a) which is rotatable around a rotation center (33c, 67c); an elastic member (32, 63) that elastically deforms by power received from the power source and thereby stores elastic energy; a transmission part (33, 67) which pushes the coated part clamp upward due to an elastic force received from the elastic member; and a restricting part (34, 68) which restricts rotation of the rotating member while the elastic member stores the elastic energy in a state in which the windproof cover is closed, and wherein the restricting part releases the elastic energy stored in the elastic member and thereby releases restriction on rotation of the rotating member in conjunction with an opening operation of the windproof cover.