A prism includes a light incident portion that has first and second convex portions, the first and second convex portions each are a convex portion that refracts rays of light incident to a prism body and reduces a spread angle after incidence to the prism body via the convex portion to be smaller than that before the incidence, the spread angle is an angle between a given two of the rays, a first reflecting surface, provided on the prism body, that can reflect a first ray of light that has entered the prism body via the first convex portion, a first emitting portion, provided on the prism body, that emits, to the outside, the first ray reflected by the first reflecting surface, and a second emitting portion that emits, to the outside, a second ray of light that has entered the prism body via the second convex portion.