A light source device with an improved contrast ratio between a bright portion and a dark portion of a displayed image and a display divide including the light source device. In order to change a reflectance of a portion of a reflection sheet 110, 111 with gradation in response to light and dark of portions of an image displayed on a display panel 201, a control mechanism 202 arranged to control the display panel 201 is provided. A first storing mechanism 104 and a second storing mechanism 105 arranged to store signals generated by the control mechanism 202, a calculation mechanism 103 arranged to calculate reflectances of portions of the reflection sheet 110, 111, a third storing mechanism 106 arranged to store the reflectances calculated by the calculation mechanism 103, and a reflectance control mechanism 107 arranged to control the reflection sheet 110, 111 based on the reflectances are provided.