There are provided a blade drive device and an optical instrument. The blade drive device includes a substrate that has an opening, a front curtain and a rear curtain that are movable along an opening surface of the opening so as to open and close the opening, a front curtain locking portion that interlocks with opening and closing operations of the front curtain, a rear curtain locking portion that interlocks with opening and closing operations of the rear curtain, a regulation lever that is configured to be pivotally movable around a lever axis, that enters an operation trajectory of the front curtain locking portion and the rear curtain locking portion, and that is capable of entry and escape between an entry position for regulating the movement of the front curtain and the rear curtain in a closing direction and an escape position escaped from the operation trajectory, a regulation electromagnetic actuator that is configured to be rotatable around a regulation axis, and a linkage lever that causes the regulation lever to pivot around the lever axis in response to the rotation around the regulation axis of the regulation electromagnetic actuator. The regulation lever and the linkage lever engage with each other while being provided with play in a circumferential direction around the regulation axis.