PURPOSE: To enable the transfer of ready-mixed concrete or the like that is less in pulsation by contacting the tip of a vane, set up free of movements to the side of a casing, slidingly the circumferential surface of a nearly oval rotor housed in the cylindrical casing, and constituting tha vane so as to be retractable in linkage with rotation of the rotor.

CONSTITUTION: A nearly oval rotor 2 is housed in a casing with a cylindrical peripheral wall 11 free of rotation, and two spots on the circumference is slidingly contacted with an inner circumferential surface of the casing 1, driving a space in the casing 1 into two parts. A rotating cam 4 is installed in a shaft end of a turning shaft 21 fitted with the rotor 2 and, in turn, a cam follower 51 supported in the point midway in a support arm 52 is contacted with this rotating cam 4. Then, the other end of this support arm 52, whose one end is pivotally supported on an end wall 12 by a pivot 57, is connected to one end of a connecting rod 54 via a link 53, and a vane 3 is moved by motion of this connecting rod 54 via a connecting fitting 56, and then the tip is displaced so as to accord with displacement of a peripheral surface by rotation of the rotor 2 where it contacts.