To provide a reservoir which can prevent a liquid in a vessel from leaking outside via a vent structure.

In the reservoir having a breather B to communicate the inside with the outside of the vessel 1 which is provided with a labyrinth 5 for communicating the inside and the outside the vessel 1 in an outer cap 3 and an inner cap 4 for closing a spout 2 provided in an upper part of the vessel 1, and a projecting part 8 projected inward of the vessel 1 and having a vent hole 9 communicating with the labyrinth 5 in a center of the inner cap 4, a check valve 23 which permits the communication of the inside with the outside of the vessel and checks any leakage of the liquid in the vessel 1 outside the vessel 1 is provided in the vent hole 9.