Abstract: A diaphragm device for a camera having a movable lens barrel has a diaphragm blade fixedly positioned with respect to a lens mount portion, the blade being stopped down upon occurrence of shutter release. An aperture diameter setting ring is provided for presetting the rest position of the diaphragm blade when stopped down for stopping the operation of the diaphragm blade when shutter release occurs and the blade reaches a position corresponding to the aperture preset operation. Correcting means is provided for changing the rest position of the diaphragm blade in response to axial movement of the lens barrel so that the quantity of light reaching a film surface which is determined by the stopped down position of the diaphragm blade preset by the aperture diameter setting ring assumes a predetermined value irrespective of the axial movement of the lens barrel.