Abstract: A laser-machining optical apparatus designed to efficiently work an object through a large area thereof by projecting an image of a mask to the object through a laser beam having a small sectional area and a high energy density. The apparatus has a laser head for oscillating laser light for working the specimen, a mask provided in the optical path of the laser light beam between the specimen and the laser head and having a working pattern formed on its surface, an objective provided in the optical path of the laser-light beam between the mask and the specimen, a mechanism on which the mask and the specimen are placed so that an optical imaging relationship is maintained therebetween with the objective interposed therebetween, and a two-dimensional scanning device provided in the optical path of the laser light beam between the laser head and the mask to two-dimensionally scan the surface of the mask with the laser light beam from the laser head.