A front teleconverter lens system having superb optical performance with less production of aberration in spite of its compactness. The front teleconverter lens system includes, in order from an object, a first lens group having positive refractive power, and a second lens group having negative refractive power, and forming an afocal optical system. A diffractive optical surface is arranged in at least one of the first lens group and the second lens group. The conditional expression 1.2