In this study, error in the surface profile resulting from free-form surface machining using the side surface of a cylindrical tool is considered. The error is induced as a result of cutting marks on the surface of the rotating workpiece when the tool is fed continuously in the z direction. A calculation method for computer simulation is proposed for generating the surface profile from a tool path, taking account of the feed per revolution. The basic feature of the profile error is discussed using a circular cylindrical workpiece ; (a) a sectional shape of the workpiece and (b) relationships between machining conditions and the error in the surface profile are given. Numerical examples are given first for a uniform cylinder, and then a golf club represented by a physical model as an example of free-form surfaces is used.