PURPOSE: To provide the titled apparatus high in a film forming velocity due to photochemical reaction, compact in size and easy in handleability, constituted from such a structure that a discharge space forming exciting light for a photochemical reaction and a passage space for a photochemical reaction gas are surrounded by one container through a communication space.

CONSTITUTION: In a chemical vapor deposition apparatus comprising a quartz glass container 3 wherein a discharge space 4 provided with electrodes 2 and a passage space 5 flowing a photochemical reaction gas G and passing a substrate 1 are connected by a communication space 6, discharge is generated in the discharge space 4 while an electrode protective gas preventing a reaction product from adhering to the surface of the electrodes 2 is sent into said space 4 from a gas pipe 7 to generate exciting light. At the same time, the substrate 1 is heated to a desired temp. by a heater 9 in the passage space 5 and the photochemical reaction gas G is flowed to be subjected to photolysis by exciting light while the decomposed product is vapor deposited on the substrate to form a vapor deposition film at a high speed in good efficiency.