An optical system has the first, second, and third lens units from an object side. The first and third lens units have positive refractive powers. The second lens unit has a negative refractive power. The second lens unit moves toward an image side during focusing from an object at an infinite distance to an object at a finite distance. The second lens unit has a sub lens unit. The sub lens unit moves in a direction perpendicular to an optical axis to correct an image shake.