A zoom lens comprising, in order from the object side to the image side: a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit having positive refractive power; and a fourth lens unit having positive refractive power; wherein the third lens unit consists of or includes, in order from the object side to the image side a 3a'th lens sub-unit (L3a) having negative refractive power, and a 3b'th lens sub-unit (L3b) having positive refractive power; and wherein the second lens unit and the fourth lens unit move on the optical axis during zooming; and wherein the 3b'th lens sub-unit (L3b) moves in a direction having a component in the direction perpendicular to the optical axis, thereby displacing an image in the direction perpendicular to the optical axis; and wherein the 3a'th lens sub-unit (L3a) consists of or includes a negative lens element G3an both of whose major surfaces have a spherical shape, and a positive lens element, both of whose major surfaces are spherical surfaces; and wherein the 3b'th lens sub-unit (L3b) consists of or includes a positive lens element G3bp having an aspherical lens surface, and a negative lens element; and wherein the conditions of 0.25 < NG3an - NG3bp <0.51; and 0.105 < NG4p - NG3bp <0.19 are satisfied assuming that the indices of the materials of the negative lens element G3an and the positive lens element G3bp are NG3an and NG3bp respectively; and assuming that the index of the material of the positive lens element G3bp is NG3bp, and the index of the material of the positive lens element having the highest index of a material which is part of the fourth lens unit is NG4p. a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit having positive refractive power; and a fourth lens unit having positive refractive power; wherein the third lens unit consists of or includes, in order from the object side to the image side a 3a'th lens sub-unit (L3a) having negative refractive power, and a 3b'th lens sub-unit (L3b) having positive refractive power; a 3a'th lens sub-unit (L3a) having negative refractive power, and a 3b'th lens sub-unit (L3b) having positive refractive power; and wherein the second lens unit and the fourth lens unit move on the optical axis during zooming; and wherein the 3b'th lens sub-unit (L3b) moves in a direction having a component in the direction perpendicular to the optical axis, thereby displacing an image in the direction perpendicular to the optical axis; and wherein the 3a'th lens sub-unit (L3a) consists of or includes a negative lens element G3an both of whose major surfaces have a spherical shape, and a positive lens element, both of whose major surfaces are spherical surfaces; a negative lens element G3an both of whose major surfaces have a spherical shape, and a positive lens element, both of whose major surfaces are spherical surfaces; and wherein the 3b'th lens sub-unit (L3b) consists of or includes a positive lens element G3bp having an aspherical lens surface, and a negative lens element; and a positive lens element G3bp having an aspherical lens surface, and a negative lens element; and wherein the conditions of 0.25 < NG3an - NG3bp <0.51; and 0.105 < NG4p - NG3bp <0.19 are satisfied assuming that the indices of the materials of the negative lens element G3an and the positive lens element G3bp are NG3an and NG3bp respectively; and assuming that the index of the material of the positive lens element G3bp is NG3bp, and the index of the material of the positive lens element having the highest index of a material which is part of the fourth lens unit is NG4p.