In the present invention, an impeller (5) is structured with the inner ends of a subset of a plurality of vanes (6) being joined to a rotary shaft (7) and the outer ends of each vane being joined to an annular connection section (8). A pedestal (27) is formed by the bottom wall of a housing (1) protruding upwards, and has a cylindrical outer peripheral surface that corresponds to a space region inside the annular connection section. At the upper center of the pedestal, a bearing-mounting hole (28) to the inner peripheral surface of which an inner screw protrusion (28a) has been formed is provided, and a lower bearing (26) that supports the bottom end of the rotary shaft of the impeller is mounted. The lower bearing has a bearing section (31) and an outer screw protrusion (26a) that threads to the inner screw protrusion is formed at the outer peripheral surface. The position in the vertical direction of the lower bearing with respect to the bearing-mounting hole can be adjusted via the threading of the outer screw protrusion and the inner screw protrusion. The present invention is able to provide a structure for adjusting the position of the lower bearing without follow-up machining of the pedestal after injection molding and with few components.
