A laser scanning unit and a light source unit employed in the same are provided. The laser scanning unit forms a linear latent image by scanning a light beam onto a photoreceptor. The laser scanning unit includes a light source generating and radiating a light beam. An aperture substrate faces the light source and has a curved reflection surface that includes an opening and faces the light source and reflects a light beam incident on the reflection surface around the opening away from the incident axis. A beam deflector is disposed on the optical path between the aperture substrate and the photoreceptor to deflect the portion of the light beam that has passed through the aperture substrate and scans the light in a scanning direction of the photoreceptor.