A linear light source apparatus is provided, being configured to convert light emitted from one light emitting element to light extended linearly, and output thus converted light. There is a lens that diffuses light flux within a predetermined region including the optical axis of the light emitting element, out of the light incident from the light emitting element, at a predetermined diffusion angle in the second direction (x-direction). The light is made to converge with respect to the first direction (y-direction). This converts the light from one light emitting element to light extended linearly and outputs the converted light. As for the second direction (x-direction), it is possible to make the light flux sparse in the predetermined region, and in the region outside thereof, the light flux is rendered to be dense. Therefore, a distribution of light quantity in the longitudinal direction (x-direction) is implemented by controlling the light flux density, upon employing the linear light source apparatus as a light source of the image reading apparatus.