To set the specification before a shaft and a head are actually combined, by combining the shaft and the head selected from a shaft data file and a head data file and repeating the computing to obtain the primary moment and the moment of inertia.

The distribution of mass in the longitudinal direction of a plurality of existing shafts 111 is measured to make a data file. Similarly, the mass and the position of center of gravity of a plurality of existing heads 112 are measured to make the data file. ON the other hand, the primary moment and the moment of inertia from a specific point required to a golf club combining the shaft 111 and the head 112 are inputted. One of the shafts 111 and one of the heads 112 are selected respectively from the respective data files to be combined, the computing to obtain the primary moment and the moment of inertia is repeated, and the shaft and the head as the materials to be used, are determined when the result in the computing reaches an allowable value of the required specification.