An object of the present disclosure lies in that in an optical device including a blade mounted on a lens or in space in a lens, it is possible to achieve miniaturization and light weight of the entire equipped device, simplification of driving and simplification of assembling, by using a shape memory alloy in a driving portion. A blade driving device includes: a base member supporting a blade; a blade; a plate member having a caliber and constituting a blade chamber; a plate member having a caliber, constituting the blade chamber and covering the blade; a ring member rotatably shaft-supported and including a connecting portion connected to the blade; an elastic member held by the base member and the ring member; a shape memory alloy held by the base member and the ring member; a holding member for holding the shape memory alloy; and a wiring for power supply.