To provide a light shielding door open/close device whose light shielding door can be opened/closed at a sure timing and whose operability is good.

When a lens barrel 11 is inhibited from moving by an abutting part, the rotation of a gear 14c which is among the gears constituting a differential planetary gear 14 and linked with a lens barrel moving mechanism 15 is inhibited; so that driving force whose strength is equal to or more than a threshold value is transmitted to a light shielding door open/close mechanism 20 from the gear 14 and a light shielding door is opened/closed. When the lens barrel 11 is not inhibited from moving by an inhibiting means, a gear 14b which is among the gears constituting the gear 14 and linked with the mechanism 20 is prevented from rotating by a control means 22; so that the driving force is transmitted to a lens barrel driving gear train 15 from the gear 14 and the moving operation of the photographic lens barrel 11 is performed.