PURPOSE: To provide a jig which fixes an H-type steel and an L-type steel securely and solidly as component members in assembling a working frame, a timbering stand and the like.

CONSTITUTION: This assembly jig consists of a groove form part 1 and a plate form part 2, and two sets of nuts 4 are formed at both ends of the groove form part 1, the flange A of an H-type steel is held by two of bolts 3, and the flange B of an L-type steel is held by a C-type jig C to insert the flange B to projections 5 on the rear side surface of the plate form part 2.