A light source device capable of repressing light surges is fixed in a flatbed scanner to provide a light beam for scanning a document. The light source device includes a bent lamp with bent parts for generating the light beam and compensating for the brightness at two ends of the bent lamp; and a set of obscuring units fixed at the two bent parts to partially obscure the light of the lamp. Hence, the light source device can repress the light surge caused on two ends of the image sensor even if the bent parts at two ends of the lamp are very close to the sides of the scanning window. Therefore, the length of the light source device can be shortened and the width of the flatbed scanner using the light source device can also be narrowed.