Microwave is introduced into a plasma chamber of a plasma processing apparatus and magnetic field is applied thereto to allow plasma generation gas to be placed in plasma state by the electron cyclotron resonance. This plasma is introduced into a film forming chamber of the plasma processing apparatus to allow film forming gas including compound gas of carbon and fluorine or compound gas of carbon, fluorine and hydrogen, and hydro carbon gas to be placed in plasma state. In addition, an insulating film consisting of fluorine added carbon film is formed by the film forming gas placed in plasma state.