PURPOSE: To eliminate the need for executing secondary working after molding and to execute holding by a supporting frame as it is by previously forming through-holes penetrating from the front to the rear in outer peripheral part.

CONSTITUTION: This plastic sheet 1 is a sheet made of a polymethyl methacrylate and through-holes for holding are previously molded at prescribed intervals. This process for production comprises fitting a member 6 consisting of a foamed urethane resin, etc., and having elasticity to a recessed part with which a projecting part 4 formed in an upper metal 3 comes into contact. The upper metal mold 3 and a lower metal mold 5 are disposed to face each other via a gasket 7 consisting of the foamed urethane resin, etc. At this time, the projecting part 4 formed at the upper metal mold 3 is arranged in such a manner that this projecting part comes into contact with the elastic member 6 disposed on the lower metal mold 5. Acrylic syrup essentially consisting of a methyl methacrylate monomer is poured therein. This syrup is heated and cured to obtain the plastic sheet 1 having the through-holes for holding.