PURPOSE: To simplify vertical and horizontal positioning and cutouts-matching work of rails, and to accelerate connecting rails regardless of the weight of rails by operating a positioning device which is set between the ends of a pair of rails.

CONSTITUTION: An engaging portion 22 of the first side member 20 and an engaging portion 32 of the second side member 30 are made to engage rails 1 from the lower part of them. The flange portions 1 B of both of the rails 1 are transversely pressed with a transverse-pressing member 25 which is driven-by operation of a side-operating device 28, and the other sides of both rails are made to contact the second side member 30, and, thus, horizontal positioning is performed. The flange portions 1 B of both rails 1 are pressed downward with a vertical pressing member 15 which moves down by operation of an upper operating device 18, and the surfaces that face downwards are made to contact the integral engaging portions 22 and 32, and vertical positioning is, thus, performed. Then, both webs 1 A are connected with joint panels, etc.