A zoom lens comprising in order from an object side to an image side: a first lens unit (U1) configured not to move for zooming; a plurality of zooming lens units (U2, U3, U4) configured to move in zooming; a front relay lens unit (UR1) configured not to move for zooming; an extender lens unit (UEXT) insertable into and removable from an optical path for changing a focal length range of the zoom lens; and a rear relay lens unit (UR2) configured not to move for zooming, wherein an interval between each pair of adjacent lens units disposed on the object side of the extender lens unit changes in zooming, wherein a part of the first lens unit moves at focusing, and wherein following conditional expressions are satisfied: 1.00 < Def/Der / β e + 1 − few/feF < 1.75 , 0.50 < le/Der / β e < 1.22 , 0 .10 < few/feF < 1.00 , 0.10 < few/f1 < 0.80 , and 1.20 < β e < 1.80 , where few is a focal length of the zoom lens at a wide angle end in a state where the extender lens unit (UEXT) is inserted into the optical path, feF is a combined focal length from the first lens unit (U1) to the front relay lens unit (UR1) at the wide angle end, Def is an effective diameter of a lens closest to the object side in the extender lens unit (UEXT), Der is an effective diameter of a lens closest to the image side in the extender lens unit (UEXT), βe is a lateral magnification of the extender lens unit (UEXT), le is a distance on an optical axis from a surface closest to the object side in the extender lens unit (UEXT) to a surface closest to the image side in the extender lens unit (UEXT), and f1 is a focal length of the first lens unit (U1). a first lens unit (U1) configured not to move for zooming; a plurality of zooming lens units (U2, U3, U4) configured to move in zooming; a front relay lens unit (UR1) configured not to move for zooming; an extender lens unit (UEXT) insertable into and removable from an optical path for changing a focal length range of the zoom lens; and a rear relay lens unit (UR2) configured not to move for zooming, wherein an interval between each pair of adjacent lens units disposed on the object side of the extender lens unit changes in zooming, wherein a part of the first lens unit moves at focusing, and wherein following conditional expressions are satisfied: 1.00 < Def/Der / β e + 1 − few/feF < 1.75 , 0.50 < le/Der / β e < 1.22 , 0 .10 < few/feF < 1.00 , 0.10 < few/f1 < 0.80 , and 1.20 < β e < 1.80 , where few is a focal length of the zoom lens at a wide angle end in a state where the extender lens unit (UEXT) is inserted into the optical path, feF is a combined focal length from the first lens unit (U1) to the front relay lens unit (UR1) at the wide angle end, Def is an effective diameter of a lens closest to the object side in the extender lens unit (UEXT), Der is an effective diameter of a lens closest to the image side in the extender lens unit (UEXT), βe is a lateral magnification of the extender lens unit (UEXT), le is a distance on an optical axis from a surface closest to the object side in the extender lens unit (UEXT) to a surface closest to the image side in the extender lens unit (UEXT), and f1 is a focal length of the first lens unit (U1). <EOS>