A motion analysis device includes two posture angle sensors attached to a measurement object at locations distant from each other, a data acquisition section, a posture angle correction section, and a deformation amount calculation section. The data acquisition section acquires data of a first posture angle and a second posture angle respectively detected by the posture angle sensors. The posture angle correction section corrects a difference between the first posture angle and the second posture angle after starting a motion of the measurement object in accordance with a difference between the first posture angle and the second posture angle before starting the motion of the measurement object. The deformation amount calculation section calculates a deformation amount of the measurement object based on a difference between the first posture angle and the second posture angle corrected by the posture angle correction section.