A valve apparatus includes valve box, valve shaft, first flexible film, and second flexible film. The valve box includes inlet and outlet, and forms a space therein for housing the fluids. The valve shaft is inserted into through-hole formed in the wall of the valve box, and moves in the longitudinal direction of the through-hole to move valve body in order to block the flow of the fluids from inlet to outlet. The first flexible film includes a through-hole into which the valve shaft is inserted. The outer peripheral end of the first flexible film is fixed to the peripheral edge of the through-hole, and the peripheral edge of the through-hole of the first flexible film is fixed to the outer periphery of the valve shaft to close the gap between the through-hole and the valve shaft. The second flexible film forms a part of the wall of valve box.