An imaging apparatus including a first lens unit with positive power in which the most object-side surface is concave and the most image-side surface is convex, an aperture stop, a second lens unit with positive power in which the most object-side surface is convex and the most image-side surface is concave, and a third lens unit with positive power; and an image sensor. Air spacing between the second lens unit and the third lens unit assumes the shape of a biconvex air lens. The imaging apparatus satisfies the following condition: 1.4.ltoreq.|r 2R|/IH.ltoreq.15.0 where IH is the maximum photographic image height, which is a half of the diagonal length, in an effective imaging area, of the image sensor, and r 2R is the radius of curvature, measured along the optical axis, of the most image-side surface of the second lens unit.