To enable a better exposure of an antibacterial and antifungal agent on the surface of a rubber sheet by heating a non-vulcanized rubber sheet having an uneven gas-impermeable film on one or both sides thereof and an antibacterial and antifungal agent added thereinto, and curing the sheet, and then peeling off the film.

An organic peroxide curing agent and antifungal agent are added into a silicone rubber compound, and they are uniformly kneaded with two rolls to produce a composition 1. Next, calendar rolls are adjusted so as to obtain a rubber sheet of a desired thickness, and a PET film that is mat processed is passed through the calendar rolls, and while the composition 1 is being roll formed into a sheet-like shape, an integral part is fet out. The same PET film is overlaid on the obtained composition 1 so as to obtain a sandwich construction, and then it is cut into a square shape and thereafter pressed. Immediately after the pressing, the PET films tightly stuck on both sides of the composition are peeled off, and the composition is subjected to a secondary vulcanization within a dryer to thereby obtain a silicone rubber sheet.