A lens tilt adjusting mechanism includes a lens frame to which at least one lens element is fixed, a lens frame holder which holds the lens frame, axially-opposed radial surfaces formed on the lens frame and the lens frame holder, respectively, a biasing device for biasing the lens frame and the lens frame holder in directions to make the axially-opposed radial surfaces contact each other, and a protrusion formed on one of the axially-opposed radial surfaces and a recess formed on the other of the axially-opposed radial surfaces. The axially-opposed radial surfaces are in intimate contact with each other when the protrusion and the recess are engaged with each other, and the lens frame tilts relative to the lens frame holder when the protrusion is disengaged from the recess so that the protrusion is in contact with the other of the axially-opposed radial surfaces.