PURPOSE: To obtain a mechanically simple and highly efficient reflecting/refracting type zoom lens reduced at its variation of aberration due to focusing by moving a partial lens group arranged between its reflecting system and refracting system and satisfying the lens group with a prescribed condition.

CONSTITUTION: Focusing is mechanically simplified by dividing the II lens group reduced at its size and having negative refractive power which is arranged between the refracting system and the reflecting system into two lens groups having negative refractive power and moving at least one lens group to reduce the variation of aberration at the time of focusing. The I and II lens groups constitute a telephoto type lens so that its focal distance can be easily expanded and the lens diameter of the III and IVth lens groups is contracted by moving the IIIand IVth lens groups and reducing their magnification to make the whole zoom lens compact. When the focal distances of the I, II and III lens groups are defined as fI, fIIA, fIIB respectively, it is preferable to satisfy the conditions shown in the formulas to reduce the variation of aberration due to focusing and to attain the effective correction of the aberration over a wide distance up to a substance.