A diaphragm device of the present invention includes: a base plate having an aperture portion; a blade being supported by the base plate to be able to open and close the aperture portion; a drive ring being formed so as to surround the perimeter of the aperture portion, the drive ring being configured to drive the blade to open and close; a supporting pin pivotably supporting the blade being provided on the drive ring; and an engaging pin engaging with the blade and causing the blade to open or close in conjunction with the drive ring and the supporting pin, the engaging pin being provided on the base plate on an inner side of the supporting pin in the radial direction of the drive ring.