In secondary battery capacity adjustment apparatus and method for an assembled cell unit, the assembled cell unit includes: a plurality of secondary batteries; and a control board on which a capacity adjusting section is mounted, the capacity adjusting section being installed to correspond to each of the secondary batteries and configured to consume an electric power of a corresponding one of the secondary batteries to adjust a residual capacity of the corresponding one of the secondary batteries, a priority order of the secondary batteries to be capacity adjusted is determined in accordance with a mounted position of the capacity adjusting section corresponding to one of the secondary batteries on the control board and an electric power of each of the secondary batteries is caused to have consumed by the corresponding capacity adjusting section in accordance with the determined priority order to adjust a capacity of each of the secondary batteries.