Abstract: A nailing device of the present invention includes a main body, a magazine and a nail pusher. The magazine is disposed in the main body for nail units to be seated thereon. The nail pusher is slidably straddled on the magazine to push the nail units forward. The nail pusher has a first side and a second side. Two slanted guiding portions are frontward and outward extended from the two sides respectively. The slanted guiding portions have two guiding surfaces facing each other to guide and position staples, so that centers of different staples of different sizes can locate at the same position.