A valve device for a power storage device that can, when a gas is generated inside the power storage device, release the gas to the outside, and can highly prevent the intrusion of moisture from an external environment, the power storage device including: a power storage device element and a housing in which the element is housed, the valve device being attached to the housing, wherein the valve device is configured to reduce an internal pressure of the housing when the pressure increases due to a gas generated inside, and in the valve device, an amount of helium leakage from a secondary side to a primary side is 5.0×10−11 Pa·m3/sec or more and 5.0×10−6 Pa·m3/sec or less, as measured in a 25° C. environment, in accordance with a method defined in “Vacuum spraying method (spray method)” of “Method for helium leak testing” in JIS Z 2331: 2006.