To provide a compact light quantity adjusting device capable of smoothly moving a light quantity adjusting member.

The light quantity adjusting device includes: a bar-like driving member 32 arranged along a surface 37a, where an aperture 37f is formed, on a base member 37; a transmitting member 33 movable along the driving member; and the light quantity adjusting members 34 and 35 having cam groove parts 34c and 35c engaged with the transmitting member, and moving relative to the aperture by driving force received from the transmitting member, which moves, through the cam groove parts so as to change passing light quantity. An electromechanical energy conversion element 31 making the driving member vibrate is connected to one end of the driving member. The transmitting member is driven along the driving member by coming into contact with the vibrated driving member.