PURPOSE: To produce a dense metal oxide film in a short time by forming a metal oxide porous film on one side of a cylindrical porous substrate and then supplying a gaseous metal halide on a film forming surface and an oxygen- contg. gas from the opposite side.

CONSTITUTION: A slurry contg. a metal oxide is applied on one side of a bottomed cylindrical porous substrate, dried and heat-treated at about 1400-1500°C to form a porous film of the metal oxide. The porosity of the porous film is preferably controlled to about 10-15% and the average pore diameter to about 0.02-1μm. The substrate 8 coated with the porous film 7 is placed in a reaction furnace 6. The furnace is kept at a specified temp. by a heater 11, and the gaseous halide of a metal constituting the metal oxide formed from a gaseous halide from a gas controller 9 and the vacuum source 12 is supplied. An oxygen-contg. gas is simultaneously supplied from the opposite side of the porous film forming surface of the substrate 8 through an oxygen feed passage 14. As a result, a metal oxide is deposited in the porous film 7 or on its surface.