A gas purge unit includes an intake nozzle 28, a pivotable body 31, and an O-ring 35. The intake nozzle 28 has a nozzle opening 26 flowing out a cleaning gas. The pivotable body 31 is arranged in a ring shape to surround a cylindrical projection 28b of the nozzle 28, and is provided with a contact part 34 formed on a tip portion of the pivotable body 31 to be able to detachably contact with the intake port 5. The ring-shaped O-ring 35 is held to be compressively elastically deformable along a longitudinal direction of the cylindrical projection 28b between a rear end of the pivotable body 31 and a base portion 28a of the nozzle 28.