Provided is an endmill. The maximum spindle speed, per one minute, of a main spindle to which the endmill is attached is Smax. The number of teeth of the endmill is N. The outer shape of the endmill is Da. The natural frequency at which vibrations at the end of the endmill reach a maximum level is ω1. ω1 and/or N are set so that when the diameter-direction infeed amount of the endmill is set to Rd: i) ω1×60/N×6<Smax, if Rd is at least 4% of Da; and ii) ω1×60/N×3<Smax, if Rd is less than 4% of Da.

A tool selection unit has an analysis unit and a selection unit. The analysis unit determines a pick feed direction and the feed direction of a tool on the basis of information relating to the shape of a machining region including a double curved surface or a machining surface in the machining region, and creates parameter information in which at least a value relating to the smallest curvature radius in the machining surface and a value relating to the largest curvature radius in the pick feed direction are recorded. The selection unit selects a tool to use for machining the machining region on the basis of the parameter information, from among a plurality of tools having a bottom cutting edge and a side cutting edge formed in a curved-surface shape having a curvature radius different from a curvature radius of a curved surface of the bottom cutting edge.

A tool selection unit has an analysis unit and a selection unit. The analysis unit determines a pick feed direction and the feed direction of a tool on the basis of information relating to the shape of a machining region including a double curved surface or a machining surface in the machining region, and creates parameter information in which at least a value relating to the smallest curvature radius in the machining surface and a value relating to the largest curvature radius in the pick feed direction are recorded. The selection unit selects a tool to use for machining the machining region on the basis of the parameter information, from among a plurality of tools having a bottom cutting edge and a side cutting edge formed in a curved-surface shape having a curvature radius different from a curvature radius of a curved surface of the bottom cutting edge.

Provided is an endmill (5). The maximum spindle speed, per one minute, of a main spindle to which the endmill is attached is Smax. The number of teeth of the endmill (5) is N. The outer shape of the endmill (5) is Da. The natural frequency at which vibrations at the end of the endmill (5) reach a maximum level is 1. 1 and/or N are set so that when the diameter-direction infeed amount of the endmill (5) is set to Rd: i) 160/N6<Smax, if Rd is at least 4% of Da; and ii) 160/N3<Smax, if Rd is less than 4% of Da.