A storage battery deterioration measurement device and a power storage system are provided which measure deterioration in unit batteries included in an assembled battery constituting a storage battery in a shorter time than conventional devices and systems, and which include a control unit 10 to acquire information based on the states of the multiple unit batteries 1 and a deterioration determination unit 11 to detect the unit battery 1 indicating the maximum value among the information acquired by the control unit 10 and the unit battery 1 indicating the minimum value thereamong, and to detect deterioration in the unit batteries 1 on the basis of the difference between a per-predetermined-period variation of information on the unit battery 1 indicating the maximum value and a per-predetermined-period variation of information on the unit battery 1 indicating the minimum value.