A method of measuring of the present invention includes the steps of photographing a rotating body with the curved surface having marks to obtain two-dimensional images thereof; generating a three-dimensional imaginary body with the curved surface having marks; setting an arbitrary posture of the imaginary body as a reference posture, performing a posture displacement operation in such a way that the marks of the imaginary body are coincident with the marks of the body; specifying a three-dimensional posture of the body on the basis of an amount of the posture displacement operation relative to the reference posture; and determining the rotational amount of the body and the direction of the rotational axis thereof by computing a rotation matrix relating to a rotation operation to make the three-dimensional posture of the body at one time coincident with that at another time.