Abstract: To make it possible to suppress deterioration of processing properties of a sample to be processed due to the distortion of ion sheath at the end portion of the sample to be processed or possible to maintain the condition for suppressing the deterioration, so that the acquisition rate of acceptable products can be increased, so as to thereby improve the yield. In a plasma processing apparatus, a minute hole 10 is provided in a focus ring 9 in the vicinity of the inner circumferential portion thereof. Current detecting means 11 is arranged in the bottom portion of the minute hole 10. A high-frequency power is supplied to the focus ring 9 via high-frequency power distributing means 16. A state of distortion of an ion sheath 18 is detected from an amount of current which is changed according to the amount of the high-frequency power supplied to the focus ring 9 and which is detected by current detecting means 11.