Abstract: A system for bleaching discolored teeth is provided, and this system has a function irradiating light emitted from a light-emitting section to the surface of teeth applied with a chemical agent including titanium dioxide and hydrogen peroxide, a irradiation energy of wavelength 380 to 420 nm of the light emitted from the light-emitting section is at least 37 mW/cm2 and the ratio of irradiation energy of wavelength 380 to 420 nm with respect to the irradiation energy of wavelength 200 to 800 nm thereof is at least 36% at this light-emitting section, and whereby it is possible to obtain high bleaching effect of the teeth, to reduce the heat applied to the teeth to a low level (no more than 40° C.) and to reduce emission of ultraviolet light that has an adverse effect on the human body to a low level.