To reduce pressure loss and keep a sealing performance over a long period of time by disposing a sealing member on a face of a fixed valve facing a rotary valve so as to surround each opening in the fixed valve, and setting an area of a closed part formed between the openings in the rotary valve to be larger than an area surrounded by the sealing member.

Closed parts 31d, 35 are formed larger than a region formed by one opening 22 a sealing member 24 surrounding one opening 22 of a fixed valve 21. More specifically, it is assumed that a region of the sealing member 24 surrounding the one opening in the fixed valve 21 is θ21, and regions of the closed parts 31d, 35 of a rotary valve 30 are θ31, θ35, the closed parts 31d, 35 are formed to satisfy θ31>θ21 and θ35>θ21 (herein, θ21 is the inside of the sealing member 24). Hereby, a linear part of the sealing member 24 existent between the openings 22 of the fixed valve 21 always exists in the closed parts 31d, 35 of the rotary valve 30, so that gas to be treated, treated gas, and purge gas are prevented from being mixed at the same opening. Thus, sealing performance is kept unchanged over a long period of time.