To provide a device, method and program for measuring body rocking of a subject, capable of obtaining diagnostic data related to the subject's capability of balancing, considering the actual structure of the human body.

The subject 1 is positioned at a prescribed position, and the balance of the subject is retained at the standing posture with the subject's capability of balancing. Then, photography marks 22a, 22b and 22c attached to the body of the subject are successively photographed when the subject is at the standing posture and image data are input, so that diagnostic data (a proportionality coefficient KP, an integral coefficient KI and a differential coefficient KD for the PID control) on the subject's capability of balancing are obtained from the input image data.