Actuator, light quantity adjusting apparatus, and stepping motor

A light quantity adjusting apparatus, comprising:

• a magnet which is formed in a ring shape, in which at least one surface perpendicular to a central axis thereof is divided in a peripheral direction and alternately plane-magnetized in different poles;
• a stator including a plurality of magnetic pole teeth opposed to the magnetized surface of the magnet;
• a rotor which includes an axis portion held to be rotatable about the central axis as a center, and a disk portion whose surface perpendicular to the axis portion is bonded to the magnet, and which is made of a soft magnetic material for passage of magnetic fluxes of a magnetic circuit;
• a coil which is located on substantially the same surface as that of the magnet, is fixed to the stator, and excites the stator and the disk portion;
• an output member which operates in response to rotation of the rotor;
• a base plate including an opening portion;
• and
• a light quantity adjusting member which is driven by the output member and moves above the opening portion of the base plate to change a quantity of light passing through the opening portion.