An optical path unit and a liquid crystal display device excellent in luminance in the front direction are provided. A backlight unit 2, two prism films 4a and 4b, a first polarizing plate 5, a liquid crystal cell 1 having a liquid crystal layer between a pair of substrates, and a second polarizing plate 6 are disposed in the sequence. The prism films 4a and 4b are provided with a plurality of linear prisms in parallel on a light incident surface, the linear prisms having a polygonal and tapered cross section and an endmost vertex angle of 90° to 110°. The first polarizing plate 5 and the second polarizing plate 6 are disposed such that transmission axes thereof have a crossed Nicols relationship. The prism film 4a is disposed such that the ridge lines of the linear prisms are substantially in parallel with the transmission axis of the first polarizing plate 5, and the prism film 4b is disposed such that the ridge lines of the linear prisms are substantially in parallel with the transmission axis of the second polarizing plate 6.