PURPOSE: To protect the inside surface of a casing from corrosion, facilitate replacement of the liner, and reduce the cost of manufacture by pushing the end face of the inner with a tapered surface of a connecting piece, putting the liner in pressure contact with the inner surface of casing, and thereby holding the liner solidly with the casing.

CONSTITUTION: A groove 13 is formed at the inner surface of a casing 5, and a connecting piece 12 is fitted in this groove, wherein said inner surface of casing has a form of overlapped cylinders. The end of this connecting piece 12 facing to inside the casing 5 has the sides in tapered surfaces (e) to connect with the cylindrical surfaces of the liner 9, and recesses (c), (d) on the sides are put in contact with the end face (a) and rear face (b) of the liner 9. The connecting piece 12 is screw fitted with a bolt 14 whose head is fixed at the external surface of the casing 5, and the bolt 14 is driven to draw out the connecting piece 12 outward the casing 5. Thereby the end face (a) of the liner 9 is pushed from the sides in the tangential direction so as to put the liner in pressure contact with the inner surface of the casing 5, and the inner surface of the liner 9 is faced to the rotor in connection with the tapered surface (e) of the connecting piece 12.