Abstract: A pattern forming method includes preparing a target object including silicon with an initial pattern formed thereon and having a first line width; performing a plasma oxidation process on the silicon surface inside a process chamber of a plasma processing apparatus and thereby forming a silicon oxide film on a surface of the initial pattern; and removing the silicon oxide film. The pattern forming method is arranged to repeatedly perform formation of the silicon oxide film and removal of the silicon oxide film so as to form an objective pattern having a second line width finer than the first line width on the target object.