To provide a shaft structure which prevents its own deflection with its structure.

In the shaft structure employed for a power transmission component, the shaft structure comprises a shaft member 10 formed into a hollow shape, and central portion members 11, 14 fitted into the hollow inside portion of the shaft member 10 and made up of a substance with a Young's modulus relatively larger than that of the shaft member 10. Otherwise, in the shaft structure employed for a power transmission component, the shaft structure comprises the shaft member 13 formed into a hollow shape, and the central portion member 14 filled in the hollow inside portion of the shaft member 13 with rigidity changing depending on a change in electromagnetic condition.