PURPOSE: To make the structure of a driving part simple and small-sized to facilitate setting a diaphragm mechanism into a camera body by arranging a fixed cylindrical coil and a moving permanent magnet coaxially in parallel with an aperture plane.

CONSTITUTION: A moving cylinder member 15 is inserted to a nonmagnetic material shaft 16 arranged in parallel with the aperture plane, and permanent magnets 14a and 14b are fixed to both of them. On the outside of the cylinder member 15, fixed coils 11a and 11b are fixed to a diaphragm plate 13. When a DC current is flowed to the coil 11a in this constitution, the cylinder member 15 is moved in the direction of an arrow, and the member 15 is braked and controlled by the repulsive force of the electromagnetic action between permanent magnets 14a and 14b. An mechanism 20 is driven through a moving pin 17 and a lever 18 of the cylinder member 15. Thus, the structure of the driving part is made simple and small-sized to facilitate the assembly of aperture mechanism to the camera body.