A sidelight-type backlight module includes a casing body, a light-guiding plate, a reflector plate, a light-emitting unit, and a reflector component. The reflector plate is disposed at a surface of the light-guiding plate, and has an extension part extending beyond a side edge of the light-guiding plate that faces toward the light-emitting unit. The reflector component has a light-reflecting face spaced apart from the reflector plate. The light-emitting unit is disposed between the extension part and the light-reflecting face. The extension part and the light-reflecting face reflect light of the light-emitting unit into the light-guiding plate so that a lamp reflector can be omitted. Preferably, the reflector component is formed integrally with the casing body.