Provided is a light source unit that emits linear light to an original, the light source unit including: light sources that emit light; a light guide that is formed in a rod shape and that guides the light from the light sources to the original; a frame that houses the light sources and the light guide; and a circuit board including a conduction portion electrically connected to the light sources, wherein the circuit board is provided with a slit in a longitudinal direction of the light guide, the slit is disposed closer to the original than the light guide, and the light from the light guide is emitted to the original through the slit.