This invention provides an imaging optical system that can prevent blocking of a desired imaging light flux and prevent generation of unwanted ghost light. The imaging optical system includes: a first lens array that includes a plurality of lenses arrayed in a first direction and that forms an intermediate image of an object in a first section parallel to the first direction; a second lens array that includes a plurality of lenses arrayed in the first direction and that re-images the intermediate image of the object in the first section; and a light blocking member disposed between optical axes of adjacent lenses of the first and second lens arrays. At least one of the first and second lens arrays has a ghost light suppressing portion between adjacent lens surfaces. A width of the ghost light suppressing portion in the first direction is greater than a width in the first direction of the light blocking member.