This paper addresses a trajectory tracking problem of mechanical systems with obstacle avoidance. Our strategy to improve obstacle avoidance is based on the field potential method using an existing navigation function. However, direct application of this function to trajectory tracking can hinder obstacle avoidance. We newly introduce a parameterized function representing a reference trajectory and propose a feedback law to control the parameter, thereby ensuring effective obstacle avoidance. Successful trajectory tracking is achieved by the convergence of the coordinates of the systems to the parameterized function. Because our method adopts a bounded navigation function, the proposed controller produces a bounded input signal even when the coordinates approach obstacles. Finally, a simulation of a two-link manipulator illustrates the effectiveness of the proposed method.