A valve device opens/closes an opening that is located at an end portion of a flow path and whose shape is a point symmetrical or substantially point symmetrical planar figure. The valve device includes a lid portion closing the opening and an arm portion rotating the lid portion about an axis to open/close the opening. A straight line passing through the center of the opening and orthogonal to the opening is taken as a center line. The axis is a straight line intersecting the flow path without intersecting the center line. When closing the opening, the arm portion rotates the lid portion toward the center line, and when opening the opening, the arm portion rotates the lid portion to the opposite side of the center line.