An object to provide an insulating film for a semiconductor device, which has characteristics of low permittivity, a low leak current, and high mechanical strength, undergoes small time-dependent change of these characteristics, and has excellent water resistance, and to provide a manufacturing apparatus of the same, and a manufacturing method of the semiconductor device using the insulating film. The production process comprises a film forming step of supplying a mixed gas containing a carrier gas and a raw material gas, which is a gasified material having borazine skeletal molecules, into a chamber, causing the mixed gas to be in a plasma state, applying a bias to the substrate placed in the chamber, and carrying out gas-phase polymerization by using the borazine skeletal molecule as a fundamental unit so as to form the insulating film on the substrate; and a reaction promoting step of, after the film forming step, bringing the bias applied to the substrate to a different magnitude from the bias in the film forming step, supplying the mixed gas while gradually reducing only the raw material gas, which is the gasified material having the borazine skeletal molecules, treating the insulating film with a plasma mainly comprising the carrier gas.