PURPOSE: To transfer a viscous fluid in constant stable flow without generating pulsation.

CONSTITUTION: The inner peripheral surface of a casing 11 for enclosing plural vanes 14, 15 and a rotor 10 is formed of a first to a fourth inner peripheral surface 25-28. The first inner peripheral surface 25 is the circular arc face of a radius R1 with a rotation axis 8 as the center, and the second inner peripheral surface 26 is the circular arc face of a second radius R2 smaller than the first radius R1 with the rotation axis 8 as the center. The third inner peripheral surface 27 is the circular arc face of a radius R3 connecting the respective end parts of the first and second inner peripheral surface 25, 26, and the fourth inner peripheral surface 28 is the circular arc face of a radius R4 connecting the respective end parts P3, P4 of the first and second inner peripheral surface 25, 26. The inner diameters, passing the rotation axis 8, of the respective inner peripheral surface 25-28 are made the same as the length L1, L2 of vanes 14, 15.