A blind spot area warning and illustrating device includes a light guiding member including a light output face and a light incident face having grooves. The light guiding member further includes an operating face opposite to the light output face and having reflective faces. Each reflective face is at an acute angle to the light output face. A cover is mounted around the light guiding member. The light output face of the light guiding member is aligned with a light transmitting area of a mirror of a side view mirror. A light emitting diode lamp is mounted in the cover and is aligned with the light incident face. When the light emitting diode lamp is activated to emit light, the grooves diffuse the light emitted by the light emitting diode lamp, and the reflective faces reflect the diffused light to uniformly pass outwardly through the light output face.