[en] Purpose: To improve energy efficiency of uranium 235 by making two or more lines of a hyperfine structure of an electron excitation level of the atom coincident with oscillation lines of a chromatic laser. Constitution: The level 7s7p⁷M₇, which is an important level for concentrating uranium, includes eight levels, namely F = 21/2, F = 19/2, F = 17/2, F = 15/2, F = 13/2, F = 11/2, F = 9/2 and F = 7/2. Also, by setting the interval of laser oscillation lines to 0.5 GHz and bringing the oscillation line of the lowest wavelength into coincidence with the level F = 21/2, other laser oscillation lines coincide with the levels F = 17/2, 11/2 and 7/2. While in the prior-art method using only a single hyperfine structure line the level F = 21/2 is used, by setting the sectional area of excitation of the level to 1 the sectional areas of excitation of the levels F = 17/2, F = 11/2 and F = 7/2 are respectively 0.8, 0.52 and 0.33. Thus, by using these levels according to the invention an energy efficiency of about 2.7 times that according to the prior-art can be obtained, and it is possible to obtain an energy efficiency on the order of twice the prior-art value even if various conditions are taken into consideration. (Kamimura, M.)