PURPOSE: To improve durability by suppressing inferior lubrication and reduction wearing an oil seal while the oil seal is made so as to come into slide contact with almost the same circumference.

CONSTITUTION: Respctively between both end parts of a case 53 and a rotary shaft 4, a plurality of labyrinth seals 7, 8, bearing 33 and oil seal 16 are interposed successively from inside the case 53, also to provide a plurality of the labyrinth seals 7, 8 so as to be individually received to an annular groove of the case 53 with an internal peripheral surface elastically closely attached to a peripheral surface of the rotary shaft 4, further to cut one part in a peripheral direction of each labyrinth seal 7, 8 by a cut section tilted from the center axial line, to form a bias cut part, so as to form an opening by the bias cut part in a condition of substantially no pressure further at an ordinary temperature.