In a backlight module, a diffusive structure and a prism structure are replaced by a diffusive prism film formed on a substrate and transferred via In-Mold Decoration by Roller (IMR) to a light guide body via injection molding. A reflection film is also transferred to an opposite side of the light guide body via the same way. In such way, optical films may be readily transferred to the light guide body via two-side IMR during the process of injection molding of the light guide body, saving room taken by substrates of the optical components.