A method for continuously forming a functional deposited film with a large area according to a microwave plasma CVD process is described. The method comprises the steps of continuously traveling a band-shaped member containing a conductive member along its length during which a pillar-shaped film-forming space capable of being kept substantially in vacuum therein is established by the use of the traveling band-shaped member as a side wall for the film-forming space, charging starting gases for film formation through a gas feed means into the film-forming space, and simultaneously radiating a microwave through a microwave antenna in all directions vertical to the direction of movement of the microwave so that microwave power is supplied to the film-forming space to initiate a plasma in the space whereby the film is deposited on the surface of the continuously traveling band-shaped member which constitutes the side wall exposed to the plasma. An apparatus for carrying out the method is also described.