To simply and securely tighten or loosen abutting ribs 9, 9' for assembly in a narrow corner part 8 of an assembly type structure by a bolt.

A wrench device is constituted by juxtaposing a plurality of gears 2 meshing mutually in the longitudinal direction between rectangular parallel boards 1 and 1, drilling a wrench hole 4 in rotary shafts 3, 3 provided protrudedly on both faces of at least the gears 2 at one end and the other end, supporting the rotary shafts 3, 3 in bearing holes 5, 5 idly drilled in the parallel boards 1, 1, arranging a check claw 6 on the gear 2, and combining with a socket wrench 7 engaging with the wrench hole 4 detachably.