To prevent a front frame from being easily opened without damaging the surface of an exhibit or an acrylic plate arranged on the surface and without using a special tool when the front frame is opened.

A holding portion 13 of the front frame 9 is fitted to a shaft 8 of a base frame 2 to make the front frame 9 turnabe inward and outward. The front frame 9 is bent to make an inner end 10 and an outer end 11 have an axial cross-section of a truncated chevron shape with respect to a body portion 12. A cam 13a having a cross-section of a right angle shape is formed on the inside portion of the holding portion 13 of the front frame 9. An expansive pressure spring member 14 is contractedly provided between a receiving piece 5 receiving the peripheral edge of an exhibit on the base frame 2 and the holding portion 13 of the front frame 9. The base frames 2 are assembled into a rectangular frame by metal connector 15. A concavity 11A having a necessary depth directed diagonally inward is formed at a bent base of an outside portion 11 in the front frame 9.