To provide an imaging optical system that has a miniaturized and thinner physical size and excellently corrected aberrations including a magnification chromatic aberration.

The imaging optical system has a positive lens group G1 on the side nearest to an object, an aperture stop, and a cemented lens that is formed of a plurality of lenses cemented by a second or a third positive lens group GR from the aperture stop further toward an image side from the aperture stop. In an orthogonal coordinate system in which νd denotes a lateral axis and θgF denotes a longitudinal axis, when a linear line represented by θgF=α×νd+β (where α=-0.00566) is set, the imaging optical system includes θgF and νd of at least one negative lens LA constituting the cemented lens in both of an area defined by a linear line at a lower limit and a linear line at an upper limit in a range of a conditional expression (1), 0.7600<β<0.9000, and an area determined by a conditional expression (2), 12<νd<30.