Plasma processing method

A plasma processing method of processing a processing target object, in which an organic film, a mask film and a resist film are stacked in sequence, by plasma includes a process of supplying a modifying gas, which is a H2 gas, a hydrogen halide gas, or a mixed gas containing a rare gas and a H2 gas or a hydrogen halide gas, into a chamber accommodating therein the processing target object in which a preset pattern is formed on the resist film; and modifying process of modifying the resist film of the processing target object by plasma of the modifying gas at a processing temperature equal to or less than −20° C.