A recessed portion forming method for forming a plurality of recessed portions in a thermally deformable heat mode recording material layer is provided, which method includes: a recessed portion forming step of applying condensed light emitted from an optical system including a light source, to the recording material layer to form the recessed portions; an inspection light illumination step of applying inspection light to the recessed portions during or after formation of the recessed portions in the recording material layer; a detection step of detecting a light quantity of the inspection light reflected or diffracted from the recessed portions; and an output regulation step of regulating an output of the light source based upon the light quantity so that the light quantity becomes a predetermined value. Methods for manufacturing a pit-projection product, a light emitting element, and an optical element, using this method are also provided.