PURPOSE: To improve workability in assembling of the title device by fixing joint strips in grid shapes to a ceiling structure, and by installing each one cf panels to each one box of the grids with hook-shaped projections provided to edge frames of the panels inserted into slits that are provided to the joint strips.

CONSTITUTION: Joint strips 11..., 12... are fixed lengthwise and crosswise to a ceiling structure so that the joint strips are formed in grid shapes, and two- lined slits are provided to either of the joint strips that extend lengthwise or crosswise. Four sides of a panel 13 are folded toward the reverse side of the panel, and thereby edge frames 16a-16d are formed. Hook-shaped projections 17 are provided to the two edge frames 16a, 16c that are facing each other. Each of the panels 13 is installed to the joint strips 11..., 12... of each one box of the grids by inserting the hook-shaped projections 17 into the slits. Metals 14 for fixing the panels are then fixed to the joint strips 11..., 12... so that the panels 13 can be prevented from moving.