A light guide device (21) includes an incident surface (211), an emitting surface (212) and a plurality of protrusions (212a). The incident surface is configured so as to allow an incident light to pass therethrough. The emitting surface is adjoining the incident surface and configured so as to allow the light to emit out of the light guide device. The protrusions are formed on at least a portion of the emitting surface. The protrusions are configured for concentrating light that emits out from said portion of the emitting surface. The present application is also concerned to a backlight module (2) including a light source (22) and the light guide device.