Multiple target tracking is a challenging problem, especially when targets are frequently crossing each other. It becomes very difficult and confusing when some targets are often occluded by other targets. This paper proposes a novel tracking method for the problem using an appearance-based condensation tracker. In order to overcome difficulties in the occlusion problem, a target object is regarded as a set of parts that constrains each other in the target structure. While each part is tracked basically in the condensation method, all the parts cooperate in the drift step of the condensation. Experimental results show the effectiveness of the proposed method for multiple person tracking and human face tracking.