PURPOSE: To measure the original shaft flexibility of a club of each number with extremely high precision by providing a supporting means which supports one end part of the club shaft fixedly, a pressing means which flexes the shaft to specific size, and a reaction force measuring means which measures and displays the reaction force of the shaft.

CONSTITUTION: Titled flexibility measuring instrument 12 consists of the supporting means 13 which supports the club 1 to be measured fixedly, the pressing means 14 which flexes the shaft 11 of the club 1, and the reaction force measuring means 15 which measures the reaction force of the shaft 11 flexed by the pressing means 14. The supporting means 13 supports the grip end 10 of the club 1 fixedly by a screw 16 and the base 17 of the supporting means 13 is allowed to project out of and enter the lower part of the main body 18 freely. The pressing means 14 presses the shaft 11 by a pressing member 23 to lower the position of support length L, i.e. loading point, P, flexing the shaft 11 to the specific size l. The reaction force measuring means 15 is arranged over the main body 18 and the measuring means 15 consists of a balance, i.e. spring balance associated with the driving lever 24 of the pressing means 14.