An attachment for a nailing machine in which a nose part drives out a nail having a nail head portion and a nail shaft portion, and in which a driver repeatedly strikes the nail, includes: a holder removably attached to the end of the nose part; nail guide members oppositely disposed on the end of the holder with respect to the center axis of the nose part, each of the nail guide members including, a first guide surface provided on an inner side thereof increasing in diameter in a taper form toward the holder, for guiding the nail head portion driven out from the nose part, a second guide surface provided continuous with the first guide surface, an inner diameter of the second guide surface being the same as or smaller than the diameter of the nail shaft portion, wherein the entire circumferential surfaces of the nail head portion and the nail shaft portion are guided by the first and second guide surfaces, and an outer surface tapered such that the outer surface narrows toward the end edge of the second guide surface; pivot shafts provided perpendicular to the center axis of the nose part, the pivot shafts open/closably supporting the respective nail guide members; and urging device for urging the nail guide members toward the center axis of the nose part.