A method of controlling film thickness of dielectric multilayer film with high precision, an optical film thickness controlling apparatus and a dielectric multilayer film manufacturing apparatus that can control the film thickness. An optical film thickness controlling apparatus includes a film formation device having a rotatable substrate and a sputtering target, a photodiode that detects each of a plurality of monochromatic light beams applied to the rotatable substrate along a radius thereof at predetermined intervals, in which a movable shutter that moves along the direction of the radius of the rotatable substrate to shut off film formation on the substrate between the substrate and the target. From each of the monochromatic light beams, a quadratic regression function of reciprocal transmittance is calculated by a least squares method, and a CPU and a motor driver move the movable shutter to shut off the film formation at the film formation region.