PURPOSE: To prevent oil from spilling from the labyrinth seals of a bearing box to its inner chamber side, even though the suction pressure of an air blower is applied to its inner chamber side.

CONSTITUTION: On the end part of a rotating machine 10 through which a shaft 11 is passed, a bearing box 14 which supports a bearing 13 by storing oil in it is provided. On the inner chamber side of the bearing box 14, first and second labyrinth seals 16, 17 are provided sandwiching a compartment 15 between them, and the compartment 15 is exposed to the suction side of an air blower 19. A third labyrinth seal 4 is formed out of the end of a ring-like body 1 extended from the air blower 19 and the end surface of the bearing box 14, and in its turn, an auxiliary compartment 5 is constituted on the inside of the ring-like body 1. The compartment 15 and the auxiliary compartment 5 are connected with the pressure side of the air blower 19 by pressure pipes 2a, 2b respectively, and the compartment 15 is opened to the atmospheric air by an atmospheric air pipe 3. Thereby, the auxiliary compartment 5 and the compartment 15 are released from the suction pressure of the air blower 19, and the oil spill of the bearing box 14 is prevented.