We discuss a force control problem for a constrained one-link flexible manipulator based on distributed parameter model. The proposed control law consists of bending moment at the root of the flexible manipulator and its derivative, which regulates simultaneously the force and the rotational angle of the motor without the angle and the force information. And it ensures the asymptotic stability of the closed-loop system. As the control law is derived based on the distributed parameter model, we can avoid the drawbacks resulting from finite dimensional approximation.