A restraining roller of a hook winch has a roller middle part and first and second roller end parts. The roller middle part is formed in a columnar shape. Each of the first and second roller end parts is formed in a roughly circular truncated cone shape. The widths of the first and second roller end parts are greater than the diameter of a wire rope. A difference in diameter between an inner end and outer end of each of the first and second roller end parts is less than the diameter of the wire rope. Taper angles of the first and second roller end parts are different from each other.