A blade drive device according to a first embodiment includes: a board including an opening and a slide slot; a blade for adjusting an opening amount of the opening; and a transmitting member for transmitting a drive force from an electromagnetic actuator to the blade through the slide slot. The transmitting member includes: an arm member revolving; and an engagement member sliding in contact with an inner surface of the slide slot in conjunction with a revolving of the arm member, and being brought into pressure contact with the inner surface of the slide slot by an external impact.