In the present invention, a valve device comprises the following: a butterfly and a first link member supported by a stay so that each are rotatable and movable about a first rotation axis line and a second rotation axis line; a second link member supported by the butterfly so as to be rotatable and moveable about a third rotation axis line; and a spring for impelling the butterfly in the closed valve direction. The first link member and the second link member are connected so as to be mutually rotatable and movable about a fourth rotation axis line. The angle formed by the first link line connecting the second rotation axis line and the fourth rotation axis line and the second link line connecting the third rotation axis line and the fourth rotation axis line is formed to be largest in the state where the butterfly valve is closed.