A light-adjusting unit includes: a pair of light-shielding plates arranged about an illuminating optical axis of an incoming light flux and configured to block the light flux in response to the amount of rotation; a pair of rotation transmitting gears configured to hold and rotate the pair of light-shielding plates respectively; a pair of supporting shafts configured to rotatably support the pair of rotation transmitting gears respectively; a supporting substrate on which the pair of supporting shafts are provided; and a pair of urging members configured to press and urge the pair of rotation transmitting gears respectively against the supporting substrate.