Recently, with the aging of the population, fall accidents of elderly people are increasing. In order to reduce fall accidents, it is necessary to detect the walking ability decline of elderly people. People with medical knowledge, such as physiotherapists, qualitatively evaluate and judge walking ability from experiences and tendencies by a walking test. However, in this case, it is difficult to examine many subjects and to evaluate them quantitatively. Therefore, it is increasing to the demand for walking measurement systems using instruments. Requirement of this system is not that it can be measured with high accuracy but that it is simple, inexpensive and accurate enough for gait ability evaluation. Therefore, three-dimensional motion analysis device that are high accuracy but expensive and need to be equipped with markers are not suitable.