We have formulated a successive three-link and three-joint optimal control model that reproduces human squat movements. The model successively optimizes the half-crouching process and the rising-up process of squat movements, and its criterion function consists of three kinds of energy costs, an center-of-gravity cost, and an input (torque-change) cost. We clarify its fundamental performance and factors indispensable for reproducing the same squat movements as humans. Consequently, the following results were obtained: (1) experimentally measured squat movements were successfully reproduced by appropriately adjusting the switching time when the half-crouching process ends and the rising-up process starts; (2) the energy costs and the center-of-gravity cost hardly affected the model's performance; (3) there existed the optimum switching time for each squat condition. These results suggest that the proposed model is effective as a model of the human squatting mechanism and that the switching time can be a factor involved strongly in human squat movements.