A closed space is formed in a reduced pressure drying station, and the closed space is brought to a vacuum state. In this state, an EB unit irradiates a wafer mounted on a hot plate with an electron beam to foam an insulating film material. Subsequently, the hot plate is raised to a predetermined temperature, and drying processing is performed under a reduced pressure. As described above, since the foaming processing is performed in the reduced pressure drying station, bubbles remain in the insulating film, so that the existence of the bubbles can decrease the relative dielectric constant.