PURPOSE: To provide a focusing system suitable a zoom lens.

CONSTITUTION: In this zoom lens having a first lens group G1 having positive refracting power, a second lens group G2 having negative refracting power, a third lens group G3 having positive refracting power, and a fourth lens group G4 having positive refracting power in this order from an object side, and performing variable power from a wide angle end to a telephoto end by respectively changing an air interval between the G1 and the G2, an air interval between the G2 and G3, and an air interval between the G3 and G4; focusing from a long distance to a short distance is performed by integrally moving the G2 and the G3 toward an image surface direction.