PURPOSE: To increase unifying force of a plate material with a frame body by preventing a nail from projecting from the frame body owing to bend of the nail with a conventional nailing machine by a method wherein a nail-driving in direction is made changeable in the nailing machine which drives automatically the nail to be drawn out into the frame body.

CONSTITUTION: A roller 31 of a frame moves to a position 31a along a cam groove 29 when a piston rod of one side cylinder advances leftward. Therefore, a nailing machine 9b comes to be inclined to a position 9b1 of a two-dot chain line as a whole, and a nail-driving in direction B comes to be inclined by an angle θ1 from the perpendicular direction A. Besides, when another cylinder of the dual cylinder is actuated and the piston rod moves back relatively, the roller 31 is moved to a position 31b thereby. Therefore, the nailing machine 9b is inclined to a position 9b2 of the two-dot chain line, and the nail-driving in direction C comes to be of a state of being inclined by an angle θ2 on an opposed side to the angle θ1.