A light source unit includes a holder, a light source, coupling lens, and a support member. The light source is supported by the holder and projects a light beam against a target. The coupling lens adjusts an optical axis of the light beam. The support member contacts the holder and the coupling lens to fix the coupling lens in place on the holder after the coupling lens adjusts the optical axis of the light beam. The holder and the coupling lens are adhered to the support member using an adhesive agent. An optical scanner includes a rotary deflector to deflect and scan the light projected from the light source unit, a scan optical element to focus the light deflected by the rotary deflector, and the light source unit. An image forming apparatus includes the optical scanner.