An imaging optical system includes a plurality of lens optical system rows each including a plurality of lens optical systems arranged in a first direction. The plurality of lens optical system rows is arranged in a second direction perpendicular to the first direction and to an optical axis direction. Each of the plurality of lens optical systems in each of the plurality of lens optical system rows is configured to form an erect equal-magnification image in a cross section perpendicular to the second direction and configured to form an inverted image in across section perpendicular to the first direction. Ina cross section perpendicular to the optical axis direction, optical axes of the respective plurality of lens optical systems in adjoining ones of the plurality of lens optical system rows are separate from one another in the first direction and are located on the a line.