A processing apparatus includes a processing chamber, a support mechanism provided in the processing chamber to support a wafer having an underlying film formed on a major surface and adjacent side face, and a supply member provided at the processing chamber and spaced from the support mechanism, to supply an incoming gas into the processing chamber. A gas carrying mechanism is provided for selectively sending a film forming gas and etching gas to the gas supply member. A main film is formed on a portion of an underlying film formed on the wafer supported on the support mechanism, by using the film forming gas supplied from the gas supply member. A portion of the underlying film, which is exposed, not covered with the main film, is etched away by the etching gas supplied from the gas supplied member.