Wave forces acting on a surging circular cylinder in regular waves are measured in a wave tank. Experiments are carried on various combinations of the amplitude of a wave and a surge, and the phase difference between them. The results of experiments are compared with those of calculations. The Morison equation extended to the case of relative motion is employed to calculate the forces on the cylinder. The inertia, added mass and drag coefficients used in the calculations are obtained from wave force measurements on a fixed cylinder and forced-surge tests in still water.