An optical diaphragm for adjusting an amount of an incident light beam, includes: light shielding vanes that are configured movably, and move to change an opening area enabling a passage of the light beam, thereby adjusting the amount of the light beam; an electromagnetic actuator including a coil through which a current passes, and a permanent magnet that generates a magnetic flux, moves with respect to the coil by an electromagnetic force due to an interaction between the current passing through the coil and the magnetic flux, and is connected to the light shielding vanes to move the light shielding vanes; and a position detector including: a magnetic element that outputs a predetermined voltage in accordance with intensity of a magnetic field from the permanent magnet; and an output characteristics corrector that obtains a predetermined correction parameter, and corrects output characteristics of the magnetic element based on the correction parameter.