To realize simplicity, reduction in dimensions and inexpensiveness of a light adjusting device that allows for achievement of both of a diaphragm function of adjusting a light amount and a filter function of adjusting a frequency area of passing light.

The light adjusting device comprises: two diaphragm blade members 21 and 22 that can stop down an aperture 11 to a predetermined aperture diameter; an infrared cut filter member 30 that moves between an advance position covering the aperture and a retreat position; and a drive mechanism that drives the diaphragm blade members and the infrared-cut filter member. The drive mechanism includes a drive source 60 and link members 40 and 50 that allow a diaphragm operation to be performed by moving the diaphragm blade members 21 and 22 between a fully-opened position and a fully-closed position while maintaining the infrared cut filter member 30 at the advance position in a first rotation angle range θ1 and move the infrared cut filter member 30 from the advance position to the retreat position while maintaining the diaphragm blade members 21 and 22 at the fully-opened position in a second rotation angle range θ2. Thus, the light adjusting device can be made simple, compact and inexpensive.