In a combined power system, a rotating shaft of a rotating electric machine includes a hollow cylindrical outer shaft and an inner shaft inserted into the hollow interior part of the outer shaft. The inner shaft includes a projecting distal end exposed from the outer shaft. On the projecting distal end, a rotational parameter detector, a retaining member and a restraining member are disposed. The retaining member supports the rotational parameter detector at the projecting distal end. Further, the inner shaft is restrained to the outer shaft by the restraining member.