A suitable the inner point is set on a vapor-liquid face of lubricating fluid formed in a composite capillary seal section that utilizes capillary force and rotational centrifugal force acted on the lubricating fluid. An inner peripheral surface of a ring-shaped portion is formed such that the minimum value R1 in radial-direction distances of the inner peripheral face of the ring-shaped portion becomes greater than a radial-direction distance R2 of the inner point (R1>R2). This can observe the inner point of the lubricating fluid from the immediately-above position, whereby the filling amount of the lubricating fluid can easily and surely be measured, thereby being capable of adjusting the filling amount of the lubricating fluid to a preset amount.