PURPOSE: To positively prevent the wrong operation of a liquid level detecting means even when the liquid level is largely inclined by the fluctuation of liquid stored in a reservoir body.

CONSTITUTION: The upper case 2 of a reservoir body 1 is integrally provided with a partition wall part 18, and an air reservoir part F is partitioned in the reservoir body 1 by an upper face part 4, a peripheral wall part 6 and the partition wall part 18. In the case of the liquid level being largely inclined by the fluctuation of liquid in the reservoir body 1, air in the reservoir body 1 is sealed in the air reservoir part F by the inclined liquid level. Accordingly, even when the liquid in the resevoir body 1 is largely fluctuated at the time of sudden acceleration, deceleration, or the like of a vehicle to cause the large inclination of the liquid level, the lowering of the liquid level can be suppressed by the volume part of the air sealed in the air reservoir part F so as to be able to positively prevent the wrong operation of a liquid level detecting means.