This paper presents an investigation of the drifting force acting on a sphere which is fixed or freely floating in regular waves. The theoretical drifting force coefficient C_d of a fixed sphere increases monotonically with the increasing non-dimensional wave number Ka , and agrees well with experimental data. This makes the author sure to conclude that the theory can predict correctly the drifting force acting on a fixed body. On the other hand, in a freely floating case, the theoretical C_d curve has a peak at Ka = 1.15 and this tendency is also confirmed by the experimental results. It is interesting that the peak value of C _d is greater than that value when the oncoming waves are completely reflected by the sphere. As yet the author cannot be sure to say whether this excess is still due to the part of the waves in the width of the diameter of the sphere, or to any other part. But if the latter is true, a three dimensional body for which C_d is 1.0 at a complete reflection of the oncoming waves, will presumably have a C_d value greater than 1.0, when it is freely floating in the waves.