To provides a technique capable of replenishing a working fluid smoothly while employing a method for replacing an atmospheric air with the working fluid. The reservoir apparatus (10) includes a main reservoir (20) having an inlet opening for feeding a hydraulic fluid, and an auxiliary reservoir (50) connecting thereto through a piping (30). There is a diagonally extending connecting pipe (60) at the auxiliary reservoir (50). There is a recessed portion (80) at an opening portion (64) of an inner periphery of the connecting pipe (60). This recessed portion (80), when compared with the case where there is no such a recessed portion, serves to enlarge the opening portion (64) of the connecting pipe (60) and more smoothly flow the replenishment working fluid at a nearby area of the opening portion (64). By doing so, the opening portion (64) of the connecting pipe (60) can be more enlarged at the time of replenishment of the working fluid and formation of a film of the working fluid can be prevented at the opening portion (64).
