An axial flow blood pump comprises: an impeller (2) that rotates around an axis and is provided with axial flow blades on the peripheral surface thereof, a permanent magnet inside the impeller (2), and a dynamic bearing or a pivot bearing; a first casing (5) that surrounds the peripheral surface of the impeller (2) and is provided with an intake port (11); an annular fixed element (6) that generates a rotating magnetic field in the impeller (2) and can be fitted onto the outer surface of the first casing (5); an outlet port (12); a second casing (3) that is provided with guide vanes (diffusers) (31) in the inner surface thereof; and a socket member (4) that is fittably and securely mounted onto the outer peripheral surface of the second casing (3) and is provided with a joining portion that can join with the fixed element (6).