A laser light source (1) emits a beam. A collimator lens (2) converts the beam emitted from the laser light source (1) into first substantially parallel light. A lenticular lens (3) expands a beam of the first substantially parallel light converted by the collimator lens (2) into a linear shape in a first direction. A Fresnel lens (4) converts the beam expanded in the first direction by the lenticular lens (3) into second substantially parallel light. A free curved surface mirror (5) has a reflecting surface formed into a free curved surface, and expands a beam of the second substantially parallel light converted by the Fresnel lens (4) into a planar shape in a second direction orthogonal to the first direction. This arrangement enables to provide a planar illumination device with a small thickness and high light use efficiency.