A shroud includes a body portion 5B, a mount 7 positioned at a center of the body portion 5B and supporting rotary vane wheel driver 6, and multiple support beams 10 radially extending from the mount 7 and joining the mount 7 and the body portion 5B, where each of the support beams 10 becomes thicker from an upstream side of a flow direction of air toward a downstream side thereof, and an edge portion 10ti of each of the support beams 10 on the downstream side of the flow direction of the air discharged by the rotary vane wheel 8 is oriented in a direction parallel to a rotation axis of the rotary vane wheel 8, and the edge portion on the upstream side is oriented in a direction opposite to a rotation direction of the rotary vane wheel 8.