A plasma CVD method adapted to a roll-to-roll process or the like wherein the change rate of the temperature of the substrate before and after an i-type semiconductor layer is deposited is made rapid so as to prevent diffusion of impurities occurring due to annealing, by constituting the apparatus structure in such a manner that the deposited film is formed on an elongated substrate by the plasma CVD method while heating the elongated substrate moving in an i-layer forming discharge chamber at a rate of 4.degree. C./second or higher immediately in front of an inlet to the discharge chamber and cooling the same at a rate of 4.degree. C./second or higher immediately at the outlet of the discharge chamber so that a stacked-layer type photovoltaic device having a large area and free from scattering of the characteristics is continuously formed without deterioration of the characteristics occurring due to dopant diffusion.