An impeller device may include a magnetic detecting element and a magnetic body, which is paired with the magnetic detecting element, for detecting a rotational position of a rotary impeller. The rotary impeller is formed with a bottomed recessed part having an opening into which one of the magnetic detecting element or the magnetic body is inserted, and the opening of the recessed part is sealed with resin injected by insert molding so that the one of the magnetic detecting element and the magnetic body is buried in the rotary impeller. The magnetic detecting element and the magnetic body are capable of facing to each other through a bottom face of the bottomed recessed part.