To provide a diaphragm device that suppresses the increase in the load on a motor, even if a diaphragm drive ring that is reciprocatively driven by the motor rotates a plurality of diaphragm blades in the same direction at the same time, or if the diaphragm aperture is reduced.

The six diaphragm blades 7 have blade shafts 7a and connection pins 7b, which are mounted erect, respectively, wherein the blade shaft 7a is rotatably engaged with a blade fixing hole 1c of a base plate 1, and the connection pin 7b is inserted into a cam groove 6a of the diaphragm ring 6. The blade shaft 7a and the connection pin 7b of each diaphragm blade 7 are mounted erect, inclined by a predetermined angle, in a direction orthogonal to a straight line connecting the erected mounting position of the blade shaft 7a and the erected mounting position of the connection pin 7b than the vertical state, in relation to the surface of the diaphragm blade 7, while the center lines in the axial directions of the blade shaft and the connection pin are kept in parallel and in a direction opposite to a diaphragm aperture forming edge 7c.