A method of reforming an insulating film deposited on a substrate having a recess pattern constituted by a bottom and sidewalls, includes: providing the film deposited on the substrate having the recess pattern in an evacuatable reaction chamber, wherein a property of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface of the substrate; adjusting a pressure of an atmosphere of the reaction chamber to 10 Pa or less, which atmosphere is constituted by H2 and/or He without a precursor and without a reactant; and applying RF power to the atmosphere of the pressure-adjusted reaction chamber to generate a plasma to which the film is exposed, thereby reforming the portion of the film deposited on the sidewalls to improve the property of the sidewall portion of the film.