A valve device, comprising: a shaft to rotate in response to an operation; a valve body to rotate integrally with the shaft and to have an outer peripheral surface provided with at least a part of a cylindrical surface or a spherical surface; and a housing including a valve opening in a valve chamber (α) to rotatably store the valve body, the valve opening to be opened and closed by the valve body, wherein when a direction along a radius of the shaft is expressed as a radial direction including a direction to an outer diameter and a direction to an inner diameter, a surface of the valve body facing in the direction to the outer diameter is expressed as an outwardly facing surface (25, 26 and 30), a direction in which the valve body rotates about the shaft is expressed as a rotational direction, and a surface of the valve body facing in the rotational direction is expressed as a valve-facing surface, the outwardly facing surface of the valve body is to be out of contact with the housing and the valve-facing surface is to be in contact with the housing in a fully closed state in which the valve body closes the valve opening, when the rotational direction toward a direction in which the valve body closes the valve opening is expressed as a valve closing direction, the rotational direction toward a direction in which the valve body opens the valve opening is expressed as a valve opening direction, a surface of the valve-facing surface making contact with the housing in the fully closed state is expressed as a valve seal surface (21, 22, 31 and 32), and a surface of the housing where contact with the valve seal surface is expressed as a housing seal surface (23, 24), the valve seal surface includes a first valve seal surface that protrudes in the valve closing direction and a second valve seal surface that is recessed in the valve opening direction, when a rotation center of the shaft and the valve body is expressed as a rotation axis, a distance in the radial direction from an outer diameter end of the first valve seal surface to the rotation axis is expressed as a first seal distance, and a distance in the radial direction from an outer diameter end of the second valve seal surface to the rotation axis is expressed as a second seal distance, the first seal distance is shorter than the second seal distance, and the first valve seal surface and the second valve seal surface each have at least a curved surface. a shaft to rotate in response to an operation; a valve body to rotate integrally with the shaft and to have an outer peripheral surface provided with at least a part of a cylindrical surface or a spherical surface; and a housing including a valve opening in a valve chamber (α) to rotatably store the valve body, the valve opening to be opened and closed by the valve body, wherein when a direction along a radius of the shaft is expressed as a radial direction including a direction to an outer diameter and a direction to an inner diameter, a surface of the valve body facing in the direction to the outer diameter is expressed as an outwardly facing surface (25, 26 and 30), a direction in which the valve body rotates about the shaft is expressed as a rotational direction, and a surface of the valve body facing in the rotational direction is expressed as a valve-facing surface, the outwardly facing surface of the valve body is to be out of contact with the housing and the valve-facing surface is to be in contact with the housing in a fully closed state in which the valve body closes the valve opening, when the rotational direction toward a direction in which the valve body closes the valve opening is expressed as a valve closing direction, the rotational direction toward a direction in which the valve body opens the valve opening is expressed as a valve opening direction, a surface of the valve-facing surface making contact with the housing in the fully closed state is expressed as a valve seal surface (21, 22, 31 and 32), and a surface of the housing where contact with the valve seal surface is expressed as a housing seal surface (23, 24), the valve seal surface includes a first valve seal surface that protrudes in the valve closing direction and a second valve seal surface that is recessed in the valve opening direction, when a rotation center of the shaft and the valve body is expressed as a rotation axis, a distance in the radial direction from an outer diameter end of the first valve seal surface to the rotation axis is expressed as a first seal distance, and a distance in the radial direction from an outer diameter end of the second valve seal surface to the rotation axis is expressed as a second seal distance, the first seal distance is shorter than the second seal distance, and the first valve seal surface and the second valve seal surface each have at least a curved surface.