1. An optimal process determining system comprising: a shape memory unit that stores a material shape and a product shape; a tool holder information storage unit that stores information of a plurality of tools and information of a plurality of holders; a basic tooling storage unit that stores a basic tooling composed of a combination of a tool, a holder and a tool projection length or a basic tooling template corresponding to the basic tooling for each of a plurality of machining efficiency groups; and a process determining unit that determines an optimal process, composed of a plurality of individual processes and a sequence of the plurality of individual processes, for forming the product shape from the material shape, wherein the process determining unit executes: a machined shape determining step of determining a machined shape machined by the basic tooling or basic tooling template of each machining efficiency group from the material shape; a tooling determining step of determining an optimal tooling composed of a combination of a tool, a holder and a tool projection length on the basis of information of the tools and the holders, stored in the tool holder information storage unit, the combination having a maximum machining efficiency and being able to form the material shape into a corresponding one of the machined shapes without interfering with the machined shape; a process candidate determining step of determining an optimal process candidate using the optimal tooling of each machining efficiency group; and a process determining step of determining the optimal process on the basis of the optimal process candidate of each machining efficiency group, and wherein each of the individual processes of the optimal process includes a tooling, comprising the tool, the holder and the tool projection length, and a removal region.