Generally, ball end mills are used for free-form surface machining. When machining curved surfaces with large curvature change using ball end mills, it is necessary to use tools with larger curvature of the cutting edges than the maximum curvature of the surface and minute pick feeds or to change tools for fitting the curvature of one part of the surface. However this causes poor machining efficiency. The curvature of the cutting edge of a flat end mill can be fitted to the curvature of a point on machined surfaces by adjusting the tool posture. Therefore, flat end mills can efficiently cut almost all curvature curved surfaces without tool change. This paper proposes two methods for deciding tool posture and tool path for 5-axis control machining based on minimum cusp height. To decide the tool path, one method defines tool paths along isoparametric curved lines, while the other defines tool paths along curved lines along the minimum curvature direction. The basic system was constructed based on the proposed method, and the effectiveness of the proposed method was verified.