Abstract: A nail engaging device includes a nail input chamber which is connected between the barrel and the nail box, and a plug is connected below the nail input chamber which has a plurality of holes. A cover is pivotally mounted to the barrel and has a recess defined in the inside thereof so that a front sub-pushing member and a rear sub-pushing member are pivotally engaged with the recess of the cover. A main pushing member is engaged with the holes of the nail input chamber so as to engage with the first nail. The rear sub-pushing member has a first stop extending from the top thereof and the front sub-pushing member has a second stop extending from the top thereof so that the rear sub-pushing member can be pivoted to adapt the different thickness of the two types of nails.