To provide the joint device of a panel member in a composite floor board capable of easily performing position adjustment working for the plate thickness direction of the erection plate part of a pair of joints on the joining end of adjacent bottom steel plates.

The composite floor plate joins the adjacent bottom steel plates 8 out of the panel member by the joint device 1 and is constituted by placing concrete 22 on the panel member. The joint device 1 is provided with a pair of joint bodies 2A, 2B provided respectively on the joining end of the adjacent bottom steel plates 8, an adding plate 3 attached over the surface of the erection plate part 2b of the pair of the joint bodies 2A, 2B, fixed on the erection plate part 2b by tightening means 5, 6, 7 and joining the joint bodies 2A, 2B, a position adjustment mechanism 9 for moving one joint body 2A out of at least the pair of the joint bodies 2A, 2B.