In this paper, we discuss a force control problem for a constrained one-link flexible manipulator based on distributed parameter model. The flexible manipulator is making contact with an object. In order to solve the force control problem, we propose a simple feedback control law. This proposed control law consists of bending moment at the root of the flexible manipulator and its derivative, which regulates simultaneously the contact force and the rotational angle of the motor without information of rotational angle and contact force. We prove the exponential stability of the closed-loop system by using energy multiplier method. As the control law is derived based on the distributed parameter model, we can avoid the drawbacks resulting from finite dimensional approximation.