Shaping of CO2 laser beam by Kaleidoscope, in which uniform intensity is obtained by multiple reflections, is analyzed by geometrical and physical optics. Gaussian beam is transformed into square beam spot with nonuniformity less than 2% when the beam reflects 2-3 times. Effects of angular and positional misalignments of the optics with respect to laser beam axis are also discussed. Through the analysis of the beam shaping, a novel optics has been developed, which produces rectangular-Gaussian beam spot with variable aspect ratio, unlike the case of Kaleidoscope where the aspect ratio of the beam spot is unchangeable. This optics provides higher efficiency of beam shaping and higher absorption in metal working by utilizing plane-polarized laser beam. Laser-surface hardening is demonstrated without absorption coating by using this optics.