A separator disposing portion 15 is provided with a ball screw 22 and an arm 23. The arm 23 is a member which comes into contact with a holder 17 and a separator disk 18, thereby allowing them to move. The arm 23 is provided with a chuck portion 30 which is connected to a piston 29 and can be fitted to a chuck pedestal 27. The chuck portion 30 comes close to or moves away from an expansion/contraction shaft 16 in association with expansion and contraction of the piston 29. Further, the chuck portion 30 comes into contact with an outer circumference surface of the holder 17, a side surface of the holder 17 and a side surface of the separator disk 18 in association with movements of the piston 29 and a driving portion 26.
