A light-amount adjusting apparatus includes two aperture diaphragms that move in such a direction that the two aperture diaphragms come close or get away with respect to an optical axis of an incident light to adjust a size of an aperture opening. At least one of the two aperture diaphragms includes an optical filter having a predetermined light transmittance characteristic. The optical filter freely advances and retreats in a direction of the aperture opening in conjunction with a movement of the aperture diaphragm.