This paper deals with the geometrical analysis of the surface roughness of a radius end milled workpiece with an inclined surface using the contouring and scanning cutter path methods. In the case of contouring, first it was classified into three types of cutting edges for generation of inclined surface. Secondly, three equations of the theoretical roughness of the machined surface were lead based on the geometrical analysis for each type. The calculation values of surface roughness almost coincide with the experimental values, therefore the validity of the analytical method is cleared. In the case of scanning, first the envelope surface of the bottom and corner edges was defined as the lower half surface of the torus. Secondly, the calculation and estimating method of the envelope curve which was obtained by the outside line of the projected torus surface is shown. The estimated values of surface roughness almost coincide with the experimental values, therefore the validity of the analytical and estimating method are cleared too. Finally, the selection of the scanning method is more effective in order to achieve highly accurate machining.