In order to develop useful assistive devices, analyses and understanding of human functions are necessary. We recorded the activities of daily living, and classified the usage of both hands using the vocabulary of ICF (International Classification of Functioning, Disability and Health) approved by WHO. We confirmed that the usage of the non-dominant hand is auxiliary and greatly different from that of the dominant hand. This indicates a possibility of a reasonable design of assistive devices, e.g. a prosthetic hand for non-dominant hand which has fewer functions but is cheaper than that for dominant hand.