An optical system including a plurality of lens units, in which an interval between adjacent lens units changes during focusing, the optical system comprising, in order from an object side to an image side, as the lens units: a first positive lens unit arranged closest to the object side; a first focus lens unit having a negative refractive power and disposed in an image side of the first positive lens unit, configured to move during focusing; an intermediate lens unit; a second focus lens unit having a negative refractive power and disposed in an image side of the first focus lens unit, configured to move during focusing; wherein the intermediate lens unit has a positive refractive power and is arranged between the first focus lens unit having the negative refractive power and the second focus lens unit having the negative refractive power; and a second positive lens unit disposed in an image side of the second focus lens unit; wherein the first focus lens unit having the negative refractive power and the second focus lens unit having the negative refractive power are configured to move toward an image side during focusing from an object at infinity to an object at short distance; characterized in that the following conditional expressions are satisfied: − 0.80 < mm 1 / fn 1 < − 0.22; and − 0.80 < mn 2 / fn 2 < − 0.22, where fn1 represents a focal length of the first focus lens unit having the negative refractive power, fn2 represents a focal length of the second focus lens unit having the negative refractive power, mn1 represents a movement amount of the first focus lens unit having the negative refractive power during focusing from an object at infinity to an object at short distance in which a magnification of the optical system is -1, and mn2 represents a movement amount of the second focus lens unit having the negative refractive power during the focusing from an object at infinity to an object at short distance in which a magnification of the optical system is -1, wherein a sign of a movement amount of the focus lens unit is positive when the position of the focus lens unit that is in focus on an object at short distance is on the image side of the position of the focus lens unit that is in focus on an object at infinity. a first positive lens unit arranged closest to the object side; a first focus lens unit having a negative refractive power and disposed in an image side of the first positive lens unit, configured to move during focusing; an intermediate lens unit; a second focus lens unit having a negative refractive power and disposed in an image side of the first focus lens unit, configured to move during focusing; wherein the intermediate lens unit has a positive refractive power and is arranged between the first focus lens unit having the negative refractive power and the second focus lens unit having the negative refractive power; and a second positive lens unit disposed in an image side of the second focus lens unit; wherein the first focus lens unit having the negative refractive power and the second focus lens unit having the negative refractive power are configured to move toward an image side during focusing from an object at infinity to an object at short distance; characterized in that the following conditional expressions are satisfied: − 0.80 < mm 1 / fn 1 < − 0.22; and − 0.80 < mn 2 / fn 2 < − 0.22, where fn1 represents a focal length of the first focus lens unit having the negative refractive power, fn2 represents a focal length of the second focus lens unit having the negative refractive power, mn1 represents a movement amount of the first focus lens unit having the negative refractive power during focusing from an object at infinity to an object at short distance in which a magnification of the optical system is -1, and mn2 represents a movement amount of the second focus lens unit having the negative refractive power during the focusing from an object at infinity to an object at short distance in which a magnification of the optical system is -1, wherein a sign of a movement amount of the focus lens unit is positive when the position of the focus lens unit that is in focus on an object at short distance is on the image side of the position of the focus lens unit that is in focus on an object at infinity.