To discharge air bubbles from a second reservoir tank which is integrally provided at the upper section of a master cylinder while securing the capacity of a first reservoir tank even when an arrangement space for the first reservoir tank separately arranged above the master cylinder is limited.

A first joint 16 at the uppermost section of the second reservoir tank 15 is connected with a second joint 17 at an intermediate position in the height direction of the first reservoir tank 14 through a first communication pipe 18, and air bubbles generated in the master cylinder 11 are discharged from the second reservoir tank 15 to the first reservoir tank 14. Also, when the height of the upper end of the first reservoir tank 14 is regulated, a fourth joint 20 at the lowermost section of the first reservoir tank 14 is connected with a third joint 19 of the master cylinder 11 through a second communication pipe 21. Therefore, a dead volume (refer to the slash section) is prevented from being caused at the lower section of the first reservoir tank 14, and the capacity of the first reservoir tank 14 can effectively be utilized.