A blood delivery port (18) is inclined upward so that a perpendicular line (X) passing the center (O &cir& _) of a centrifugal pump body (12) is positioned between two straight lines ( alpha , beta ) which connect together two circumferential joint points (A, B) in a joint portion between the blood delivery port (18) and a centrifugal chamber (15) and the centre (O &cir& _), and the centrifugal pump body (12) is supported on a driving unit (13) with a blood take-in port (17) inclined upward at an angle larger than that between an inner circumferential surface of the centrifugal chamber (15) and the axis thereof. After the centrifugal chamber has been filled with a liquid, the driving of a rotary body is done in a low-speed mode, a stopping mode and a high-speed mode in the mentioned order. According to the present invention, the stagnation of bubbles in the centrifugal chamber (15) in the centrifugal pump body (12) at the time of starting the circulation of blood to a circuit such as a pump-oxygenator can be prevented reliably.