The paper proposes the use of a cam with a reciprocating or oscillating follower for the elimination of the fluctuation of the torque input to a planer mechanism. The cam is fixed to the input shaft, which is rotating at a uniform speed, and the follower is maintained in contact with the cam by means of a spring. The expression of the input torque, which is required to drive a planar mechanism at a constant input speed, with the output leads and inertia forces considered, is derived. The cam profile is designed such that the cam input torque counters the fluctuating part of the mechanism input torque. This condition is employed in deriving the cam design equation, which is a differential equation describing the follower dsplacement. A special numerical method is proposed for the solution of this equation. Also, a formula is derived for the contact force between the cam and follower. This formula is applied at different mechanism positions, after the solution of the cam design equation, to check the contact between the cam and follower. The proposed method is applied to a four-bar linkage by using a disc cam with an oscilating follower as a numerical example.