This invention provides a numerical control method for five-axis processing machine. If the angle alpha formed between the interpolated cutting surface perpendicular direction vector (It, Jt, Kt) and the interpolated tool direction vector (Ttx, Tty, Ttz) becomes smaller, movement of a tool becomes unstable. In this case, the tool diameter compensation vector (TCx, TCy, TCz) is set to the tool diameter compensation vector calculated in the immediately previous interpolation cycle, thereby preventing unstable movement. Further, in case of a block instruction where a distance between positions in cutting point instructions is large whereas distance of movement of linear axis control point is small, an excessive cutting may occur. To deal with this problem, movement of linear axis control point in a current block is stopped or converted into linear movement so as to prevent a loop-shaped movement of the linear axis control point.