A method for continuously forming a large area functional deposited film by a microwave plasma CVD process, said method comprises: continuously moving a substrate web in the longitudinal direction; establishing a substantially enclosed film-forming chamber having a film-forming space by curving and projecting said moving substrate web to form a columnar portion to be the circumferential wall of said film forming chamber on the way moving; introducing a film-forming raw material gas through a gas feed means into said film-forming space; at the same time, radiating or propagating microwave energy into said film-forming space by using a microwave applicator means capable of radiating or propagating said microwave energy with a directivity in one direction of microwave energy to propagate to generate microwave plasma in said film-forming space, whereby continuously forming a functional deposited film on the inner face of said continuously moving circumferential wall to be exposed to said microwave plasma.An apparatus suitable for practicing said method.