An optical device guides illuminating light from a light source and includes a columnar light-guiding unit having an incidence face which the illuminating light from the light source is incident upon, an emission face which emits the illuminating light and has a larger area than the incidence face, and reflection faces which guide rays of the illuminating light which is incident from the incidence face to the emission face while bringing the rays to total internal reflection, and holders which secure the columnar light-guiding unit in position with respect to the light source, in which the columnar light-guiding unit and the holders are connected together in a single piece only on the reflection faces on the emission face side of the columnar light-guiding unit.