A process for the formation of a functional deposited film as a thin semiconductor film constituted with the group IV element or a thin semiconductor film constituted with group IV element alloy, by introducing, into a film forming space, a compound as the film-forming raw material and, if required, a compound containing an element capable of controlling valence electrons for the deposited film as the constituent element each in a gaseous state, or in a state where at least one of the compounds is activated, while forming hydrogen atoms in an excited state causing chemical reaction with at least one of the compounds in the gaseous state or in the activated state in an activation space different from the film forming space and introducing them into the film forming space, thereby forming a deposited film on a substrate, wherein the hydrogen atoms in the excited state are formed from a hydrogen gas or a gas mixture composed of a hydrogen gas and a rare gas by means of a microwave plasma generated in a plasma generation chamber disposed in a cavity resonator integrated with two impedance matching circuits in a microwave circuit and the excited state of the hydrogen atoms is controlled.