There is provided an optical system 8 for a micro analyzing system capable of precisely analyzing a sample. In the optical system 8, after light beams leaving the tip of an optical fiber 14 pass through a condensing part 13, a sample moving in a separation passage 6 due to electrophoresis is irradiated with the light beams. The condensing part 13 includes a first aspherically cylindrical surface 10 being convex toward the optical fiber 14, a second aspherically cylindrical surface 11 being convex on the opposite side to the first aspherically cylindrical surface 10, and a third aspherically cylindrical surface 12 being convex toward the second aspherically cylindrical surface 11. The first through third aspherically cylindrical surfaces 10 through 12 are arranged in that order from the side of the optical fiber 14 toward the separation passage 6. The sample moving due to electrophoresis is irradiated with light beams which are condensed by the first through third aspherically cylindrical surfaces 10 through 11 after leaving the optical fiber 14.