An RF power (Bottom RF) from a radio-frequency power source 12 is turned off (t5) and the supply of a He gas 14 to a back face of a wafer W is stopped (t5) when an end point detector 17 (EPD) detects an end point (t5), and a high-voltage DC power source 13 (HV) is turned off (t6) under the condition in which an RF power (Top RF) from a radio-frequency power source 11 is controlled to fall within a range in which etching does not progress and plasma discharge can be maintained (t5). This process enables the inhibition of the adhesion of particles while an etching amount is accurately controlled.