Abstract: A vacuum pump has an end portion and a flange extending from a periphery of the end portion. The flange portion has first and second opposed main surfaces, and first and second bolt insertion holes extending through the first and second main surfaces. An auxiliary ring is connected to the first main surface of the flange portion of the pump case. The auxiliary ring has first and second opposed main surfaces, and a third bolt insertion hole extending through the first and second main surfaces of the auxiliary ring. An auxiliary ring attaching bolt extends through the third bolt insertion hole for connecting the auxiliary ring to a chamber housing disposed opposite the end portion of the pump case. A pump case supporting bolt extends through the second bolt insertion hole of the pump case flange portion and is connected to the auxiliary ring, and a pump case fastening bolt extends through the first bolt insertion hole of the pump case flange portion and is connected to the auxiliary ring.