To provide a diaphragm mechanism that suitably operates, and optical equipment including the same.

The diaphragm mechanism includes: a diaphragm member 70 provided in an optical path of an optical system to adjust a diameter of an aperture stop; a first projection 74 provided closer to an image side of the optical system than the diaphragm mechanism to adjust the aperture of the diaphragm member by rotating around an optical axis OA; a rotating member 60 provided closer to the image side of the optical system than the diaphragm member and rotating around the optical axis OA; a second projection 62 provided closer to an object side of the optical system than the rotating member to face the first projection, and transmitting rotational force to the first projection by rotating together with the rotating member; a biasing member 76 fixed to at least one of the diaphragm member and the first projection, and biasing the second projection in contact with the second projection, to bring the first projection and the second projection into contact with each other; and a restricting member 76b provided closer to the object side of the optical system than a portion of the biasing member to be in contact with the second projection, and restricting tilt of the energizing member.