PURPOSE: To keep the selection ratio to an oxide film high, by setting the start timing of introducing wafer cooling gas to be a time point after etching is started.

CONSTITUTION: The start timing of introducing wafer cooling gas is set to be a time point after etching is started. That is, in the initial period of etching start, the wafer temperature is kept high; the deposition of reaction product is restrained; the etching of a film 304 to be etched is promoted; the introduction of cooling gas is started when etching is progressed to some extent, e.g. oxide films 302, 303 are exposed; thus the operation for restraining the etching of the oxide film is enabled. Hence the selection ratio to a silicon oxide film can be kept high by using a wafer cooling technique, without generating etching residue on a wafer step-difference part and increasing the loading effect.