The present invention relates to a deposition method of a low dielectric constant insulating film, which comprises the steps of generating a first deposition gas containing at least one silicon source selecting from the group consisting of silicon containing organic compound having siloxane bond and silicon containing organic compound having CH.sub.3 group, and an oxidizing agent consisting of oxygen containing organic compound having alkoxyl group (OR: O is oxygen and R is CH.sub.3 or C.sub.2H.sub.5), and applying electric power to the first deposition gas to generate plasma and then causing reaction to form a low dielectric constant insulating film on a substrate.