A light receiving unit including: a sensor board assembly on which plural sensor tips are arrayed in a line in a longitudinal direction of the sensor board and mounted on the sensor board; and a sensor plate on which plural of the sensor board assemblies are arrayed and mounted in a line in the longitudinal direction. The sensor chips include plural pixels formed in a line in the longitudinal direction. At longitudinal ends of the sensor board assembly, the sensor chips protrude outward in the longitudinal direction from the longitudinal ends. Between the facing sensor chips of the adjacent sensor board assemblies, the facing sensor chips mounted at the longitudinal ends, the ends of the facing sensor chips are spaced at a predetermined interval. The sensor board includes convex portions, at the longitudinal ends, protruding in the longitudinal direction. The sensor chips are mounted at the convex portion.