A duct structure, includes: a vessel forming therein a chamber, the vessel including: an inlet port, an outlet port, wherein the vessel is configured such that a fluid flows into the chamber through the inlet port and flows out of the chamber through the outlet port, and a swirling flow suppressing member disposed in a position inside the chamber adjacent to the outlet port, wherein the swirling flow suppressing member is configured to suppress a swirling flow from occurring to or adjacent to the outlet port.