A power supply system ( 1, 1#) including a plurality of power storage units ( 6-1, 6-2 to 6-N) each configured to be capable of charge/discharge, comprising: a power line ( MPL, MNL) configured to allow supply/reception of electric power between a load device and said power supply system; a plurality of voltage conversion units ( 8-1, 8-2 to 8-N) provided between said plurality of power storage units and said power line and each performing a voltage conversion operation between corresponding said power storage unit and said power line, each of said plurality of voltage conversion units being set to any one of a voltage control mode in which a voltage value of said power line is controlled to attain a voltage target value and a current control mode in which a current value of corresponding said power storage unit is controlled to attain a current target value, to perform said voltage conversion operation; actual power value obtaining means ( 2, 2#; S106, S206) for obtaining, on said power line, an actual value of electric power supplied/received to/from said load device; first determination means ( 2, 2#; S108, S208) adapted to determine which of an allowable power total value, representing a total value of allowable power of said plurality of power storage units, and said actual power value, obtained by said actual power value obtaining means, is greater; and first voltage conversion unit control means ( 2, 2#; S112, S212) adapted to set one of said plurality of voltage conversion units to said voltage control mode and setting remaining voltage conversion unit to said current control mode if said first determination means determines that said actual power value is smaller than said allowable power total value; characterized by second voltage conversion unit control means ( 2, 2#; S118, S218) adapted to set said plurality of voltage conversion units to said current control mode if said first determination means determines that said actual power value is equal to or larger than said allowable power total value. a power line ( MPL, MNL) configured to allow supply/reception of electric power between a load device and said power supply system; a plurality of voltage conversion units ( 8-1, 8-2 to 8-N) provided between said plurality of power storage units and said power line and each performing a voltage conversion operation between corresponding said power storage unit and said power line, each of said plurality of voltage conversion units being set to any one of a voltage control mode in which a voltage value of said power line is controlled to attain a voltage target value and a current control mode in which a current value of corresponding said power storage unit is controlled to attain a current target value, to perform said voltage conversion operation; actual power value obtaining means ( 2, 2#; S106, S206) for obtaining, on said power line, an actual value of electric power supplied/received to/from said load device; first determination means ( 2, 2#; S108, S208) adapted to determine which of an allowable power total value, representing a total value of allowable power of said plurality of power storage units, and said actual power value, obtained by said actual power value obtaining means, is greater; and first voltage conversion unit control means ( 2, 2#; S112, S212) adapted to set one of said plurality of voltage conversion units to said voltage control mode and setting remaining voltage conversion unit to said current control mode if said first determination means determines that said actual power value is smaller than said allowable power total value; characterized by second voltage conversion unit control means ( 2, 2#; S118, S218) adapted to set said plurality of voltage conversion units to said current control mode if said first determination means determines that said actual power value is equal to or larger than said allowable power total value.