The level set method (LSM) has attracted much attention as a method that realizes a topology free active contour modeling. This method utilizes an implicit representation of a contour to be tracked, and is able to handle the topological change of the contour intrinsically. Various applications including motion tracking and 3D geometrical modeling have been proposed so far. However, the calculation cost of reinitialization and updating of the implicit function is considerably expensive as compared with conventional active contour models such as"Snakes". To overcome this problem, we have proposed an efficient algorithm of the LSM named the Fast Level Set Method (FLSM) . This paper presents a 3D simultaneous motion tracking system of multiple targets using the FLSM, and shows a series of experimental results to verify the effectiveness of the system even in the event of occlusion. Characteristics of this system are as follows: (i) Topologically free, (ii) Robustness for self and mutual occlusion, (iii) Ease to calibrate several stereo cameras using ICP algorithm. In this paper, we present a robust 3D motion tracking system for target occlusion using the FLSM, and show some experimental results of tracking of multiple targets.