To prevent mutual pulling of a vacuum chamber 1 and a vacuum pump 2, by avoiding contraction of a vacuum pipe 3 due to negative pressure in the vacuum pipe, for example, in connecting the vacuum chamber 1 to the vacuum pump 2 through the vacuum pipe 3.

The vacuum pipe 3 has a duplex structure and supplies positive pressure to a space 3c, between an inside pipe 3a and an outside pipe 3b. Using this structure, a contraction force due to the negative pressure in the vacuum pipe 3 and an extension force of the vacuum pipe 3 due to the positive pressure are balanced, to avoid contraction of the vacuum pipe 3.