Disclosed is a light amount adjusting apparatus for an image pickup apparatus which is capable of reducing the force with which a plate member and a blade member are held in close contact with each other and driving the blade member smoothly even in a high-humidity condition. The light amount adjusting apparatus includes a base plate 5 having an opening 5a, a blade member 1 movable within a range including a position where the blade member overlaps the opening 5a in a light axis direction and restricting the amount of light passing through the opening 5a by overlapping the opening 5a, and a plate member 2 adjacent to the blade member 1 and having a cut portion 2a at a position where the plate member overlaps the blade member 1 in the light axis direction in a state in which the blade member 1 is at a predetermined position.