In this paper, the contact force control of a constrained one-link flexible arm is fully investigated using a linear distributed parameter model including the internal damping of Kelvin-Voight type. To overcome the inherent limitations caused by the non-minimum phase nature of the noncollocation of the joint torque input and the contact force output, a minimum phase transfer function is deduced by using the feedback and the output redefinition. A PD controller is then designed to accomplish the regulation of the contact force. Therefore, asymptotic tracking of a desired contact force trajectory with internal stability can be achieved. With the infinite product of transcendental functions, exact solutions of the noncollocated infinite-dimensional closed-loop force control system can be obtained so that it is free from spillover problems with stability robustness to parameter uncertainties. Numerical simulations are provided to verify the effectiveness of the proposed approach.