<p>A space between a housing (2) and a rotator (3) is hermetically sealed with a double-mechanical seal (4). A pair of rotary seal rings (41) are sandwiched between a pair of stationary seal rings (42) while sandwiching therebetween a stopper ring (44) for inhibition of relative rotation between the rotary seal rings (41) and the rotator (3). A spring (43) is interposed in a space between the stopper (44) and each of the rotary seal rings (41) for pressing each rotary seal ring (41) against the corresponding stationary seal ring (42). <IMAGE></p>
