Embodiments provide a defoaming structure of a separation device, capable of suppressing foaming of a liquid more effectively.
A defoaming structure of a separation device, according to an embodiment of the present invention, includes a cyclone including an introduction portion which includes an introduction port to introduce a liquid and a drain portion including a discharge port provided at a lower end, and a cylindrical member surrounding the discharge port at an interval and extending downward from the discharge port. The drain portion includes a first member connected to the introduction portion, a second member connected to the first member and having a discharge port provided thereon, and a first inner peripheral surface formed from the first member toward the second member and having an inner diameter decreasing downward, the discharge port includes a second inner peripheral surface connected to the first inner peripheral surface and having an inner diameter increasing downward from the first inner peripheral surface in the direction of extension, the cylindrical member includes a third inner peripheral surface surrounding the discharge port and an opening portion provided at an end, and a virtual surface on which the second inner peripheral surface extends toward the third inner peripheral surface along the direction of extension, intersects the third inner peripheral surface.