An optical apparatus for emitting a modulated beam onto an irradiated surface on a target object, comprising: an illumination optical system for collimating a laser beam into a parallel beam which is long linear in a long axis direction; an optical modulator for modulating said parallel beam into a modulated beam; and a projection optical system for guiding said modulated beam onto an irradiated surface of a target object, wherein said illumination optical system comprises a beam shaper for converting an intensity distribution of said laser beam in each of a short axis direction and said long axis direction, which is a Gaussian distribution, into an intensity distribution of said parallel beam on a modulation surface of said optical modulator in each of said short axis direction and said long axis direction, which is a top hat distribution, said projection optical system comprises a first lens; a fourth lens characterized in that the projection optical system further comprises a second lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; a third lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; wherein the fourth lens is positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens, said second lens, and said third lens, wherein said modulation surface and said irradiated surface are optically conjugated with respect to said long axis direction by said third lens and said fourth lens, and wherein said modulation surface and a front focus position of said fourth lens are optically conjugated with respect to said short axis direction by said first lens, said second lens, and said third lens, and said fourth lens is configured to condenses a beam having a top hat distribution at said front focus position onto said irradiated surface. an illumination optical system for collimating a laser beam into a parallel beam which is long linear in a long axis direction; an optical modulator for modulating said parallel beam into a modulated beam; and a projection optical system for guiding said modulated beam onto an irradiated surface of a target object, wherein said illumination optical system comprises a beam shaper for converting an intensity distribution of said laser beam in each of a short axis direction and said long axis direction, which is a Gaussian distribution, into an intensity distribution of said parallel beam on a modulation surface of said optical modulator in each of said short axis direction and said long axis direction, which is a top hat distribution, said projection optical system comprises a first lens; a fourth lens characterized in that the projection optical system further comprises a second lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; a third lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; wherein the fourth lens is positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens, said second lens, and said third lens, wherein said modulation surface and said irradiated surface are optically conjugated with respect to said long axis direction by said third lens and said fourth lens, and wherein said modulation surface and a front focus position of said fourth lens are optically conjugated with respect to said short axis direction by said first lens, said second lens, and said third lens, and said fourth lens is configured to condenses a beam having a top hat distribution at said front focus position onto said irradiated surface. a second lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; a third lens positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens; wherein the fourth lens is positioned on the forward side in the traveling direction of said modulated beam, relative to said first lens, said second lens, and said third lens, wherein said modulation surface and said irradiated surface are optically conjugated with respect to said long axis direction by said third lens and said fourth lens, and wherein said modulation surface and a front focus position of said fourth lens are optically conjugated with respect to said short axis direction by said first lens, said second lens, and said third lens, and said fourth lens is configured to condenses a beam having a top hat distribution at said front focus position onto said irradiated surface.