PURPOSE: To join joint objects each other without any necessity of penetration by providing pin parts on both sides of a flat board, inserting a pin part on one face of the flat board into one of two joint objects, and inserting the pin part on the other face into the remainder of the joint objective.

CONSTITUTION: A fixing device has such a structure that faces being struck by a hammer, when two nails are driven, are stuck together. A cylindrical auxiliary tool 2d covers a pin part 2a of the fixing device, its end 2g is struck by the hammer, etc., and the pin part 2b of the fixing device is driven into one 2e of two joint objects till a flat part 2c of the fixing device reaches the joint object 2e. Secondarily, the cylindrical auxiliary device 2d is pulled out, the other pin part 2a of the fixing device is arranged in such a state as being brought in planar contact with the other remainder of the joint objects at right angle, the rear face 2b of the joint object 2e on which the fixing device is driven by the hammer, etc., and two joint objects are joined each other. Therefore, the joint objects can be joined each other without penetrating.