An optical system includes, in order from an object side to an image side, a first lens unit having positive refractive power, and a second lens unit having negative refractive power, wherein the first lens unit moves and the second lens unit does not move during focusing, wherein the first lens unit includes a positive lens arranged closest on the object side of the first lens unit, wherein the second lens unit includes three or more lenses including at least two negative lenses, wherein the first lens unit consists of a first subunit having positive refractive power, a second subunit having negative refractive power, and a third subunit having positive refractive power arranged in order from the object side to the image side, and wherein predetermined conditional expressions are satisfied.