To fasten a connecting metal fitting in one place within several seconds by providing a holding mechanism having a pressing member provided for holding the horizontal state of a main body frame in the tip of a movable part by a button-like hooking part and fixed so as to be moved up and down.

After all connecting metal fittings ca and cb are first screwed in manually, a device is tilted forward to hook a button-like hooking part 60 in a fixing bar steel D positioned roughly on the axis of a connecting metal fitting. Then, a holding mechanism 90 is adjusted beforehand to place the device in a horizontal state, and by rotating an input end 20h in a specified direction, the metal fitting C is screwed in until it is fastened by applying specified torque, fastening in one place taking only several seconds. In this case, following the screwing-in of the connecting metal fitting C, only a pressing member 80 lowered by gravity (before pressing) stays in its position while being supported by a roller 78r because of its friction with a product surface. Then, the device is lowered automatically following the fastening of the connecting metal fitting C.