A guide wire holder, comprising: a sheath (2, 2M, 2H) having a lumen of which a central axis extends along a longitudinal axis; an operation wire which is inserted through the lumen to be able to advance and retract along the longitudinal axis; and a hook (5H, 5M) which is a member fixed to a distal end of the operation wire and has a slit formed along the longitudinal axis, the hook (5H, 5M) protruding from a distal end of the sheath (2, 2M, 2H), wherein the sheath (2, 2M, 2H) has a groove configured to extend from the distal end of the sheath (2, 2M, 2H) toward a proximal end side of the sheath (2, 2M, 2H), wherein the groove is formed to have a concave shape being recessed in a direction orthogonal to the central axis from an outer peripheral surface of the sheath (2, 2M, 2H) toward the central axis, and the groove has an inner wall surface which is a curved surface and a part of the outer peripheral surface of the sheath (2, 2M, 2H), wherein the groove forms an opening portion which opens to the outer peripheral surface of the sheath (2, 2M, 2H), wherein a bottom surface of the slit is a guide wire engagement surface (53H, 53M) of the hook (5H, 5M), wherein when seen in a front view of the distal end of the sheath (2, 2M, 2H), the groove of the sheath (2, 2M, 2H) and the slit open in directions opposite to each other, and wherein the guide wire engagement surface (53H, 53M) and the inner wall surface are configured to be capable of capturing and holding the guide wire therebetween in a state in which the guide wire engagement surface (53H, 53M) is located closer to a distal side than the groove. a sheath (2, 2M, 2H) having a lumen of which a central axis extends along a longitudinal axis; an operation wire which is inserted through the lumen to be able to advance and retract along the longitudinal axis; and a hook (5H, 5M) which is a member fixed to a distal end of the operation wire and has a slit formed along the longitudinal axis, the hook (5H, 5M) protruding from a distal end of the sheath (2, 2M, 2H), wherein the sheath (2, 2M, 2H) has a groove configured to extend from the distal end of the sheath (2, 2M, 2H) toward a proximal end side of the sheath (2, 2M, 2H), wherein the groove is formed to have a concave shape being recessed in a direction orthogonal to the central axis from an outer peripheral surface of the sheath (2, 2M, 2H) toward the central axis, and the groove has an inner wall surface which is a curved surface and a part of the outer peripheral surface of the sheath (2, 2M, 2H), wherein the groove forms an opening portion which opens to the outer peripheral surface of the sheath (2, 2M, 2H), wherein a bottom surface of the slit is a guide wire engagement surface (53H, 53M) of the hook (5H, 5M), wherein when seen in a front view of the distal end of the sheath (2, 2M, 2H), the groove of the sheath (2, 2M, 2H) and the slit open in directions opposite to each other, and wherein the guide wire engagement surface (53H, 53M) and the inner wall surface are configured to be capable of capturing and holding the guide wire therebetween in a state in which the guide wire engagement surface (53H, 53M) is located closer to a distal side than the groove.