An assembling device for attaching a light guide plate and a reflecting member together is provided. The assembling device includes a first receiving member and a second receiving member. The first receiving member defines a first recess therein for accommodating the light guide plate. The second receiving member defines a second recess therein for accommodating the reflecting member. The assembling device has an open position and a closed position. The light guide plate is capable of being loaded in the first recess and the reflecting member is capable of being loaded in the second recess when the assembling device is in the open position. The first receiving member and the second receiving member are aligned with and parallel to each other when the assembling device is in the closed position.