A triaxial acceleration sensor and a triaxial angular rate sensor are mounted on each of the lower limb portions on both sides of one joint among joints constituting a part of one lower limb of a subject. The acceleration and angular rate of each lower limb portion are measured by the triaxial acceleration sensor and triaxial angular rate sensor while the subject is walking. The orientations of each lower limb portion while walking are calculated on the basis of the measured acceleration and angular rate. A three-dimensional model including the motion trajectory of one joint is constructed by linking the lower limb portions in the calculated orientation to each other. The angle formed by the acceleration vector of one joint when the heel strikes the ground to the movement trajectory in the sagittal plane is calculated as a gait parameter.
