The invention discloses a device for reading images, a device for forming images and a device for controlling light source. The light source comprises: a detecting unit for detecting respectively the reflex light quantities of three chromatic lights emitted from a light source part and corresponding to the chromatic lights three primary colors; a light quantity proportion counting unit for counting the light quantity proportion of a reflex detected by the detecting unit; a judging unit for judging whether a light quantity proportion counted by the light quantity proportion counting is within the specified scope when the judging unit is judging a light quantity of a referent reflex of three chromatic lights shot by the light source component; and a light quantity proportion adjusting unit for adjusting respectively the light quantity proportion of the three chromatic lights shot by the light source component according to the judging result of the judging unit on the basis of the referent reflex light quantity of a light corresponding to a green light shot from the light source component.