PURPOSE: To exert capabilities over a wide range with one pump by forming a spiral groove so that its bottom face can be moved in the depth direction and providing a groove depth adjusting means changing the passage depth of the fluid flowing in the spiral groove.

CONSTITUTION: When a rotary shaft 4 is rotated, rotor blades 2 are rotated against stationary blades 3, a liquid flows into a spiral groove 6 by the rotation of the rotor blades 2, it is compressed by its viscosity, then it flows out from the spiral groove 6, and the inflow side of the fluid is set to the vacuum state. In this compression action, a groove depth adjusting means 8 which moves the bottom face of the spiral groove 6 in the depth direction and changes the passage depth of the fluid flowing in the spiral groove 6 is provided, thus this groove depth adjusting means 8 is driven to change the passage cross section area of the fluid, and pump capacity can be changed. Capacities can be exerted in a wide range with one pump.