PURPOSE: To measure exactly a moment regarding to the rotation center of an object to be measured, by deriving a distance between a position of the center of gravity of the object to be measured and the rotation center, and multiplying this distance by a weight of the object to be measured.

CONSTITUTION: A measuring instrument body 7 is supported by three load cells A, B and C. First of all, before a blade to be measured is placed on the measuring instrument body 7, outputs of the load cells A, B and C are stored in a memory of an arithmetic device 11, and a zero compensation is executed. Subsequently, the blade to be measured is placed so as to contact by pressing to a block 8, a position of the center of gravity of the blade and its angle are calculated by the arithmetic device 11. Next, a distance between the center of a rotor when this blade has been planted actually and the bottom part of the blade planted part is inputted to the arithmetic device 11 by a keyboard 13. The arithmetic device 11 calculates the distance between the center of the rotor and the position of the center of gravity, and it is multiplied by a total weight of the blade calculated from a total of a load working on each load cell A, B and C, by which a moment of the blade to the center of the rotor is calculated.