A power source system for an electric powered vehicle chargeable by an external power source outside of the vehicle, comprising: rechargeable main power storage device and sub power storage device; a charger for converting electric power supplied from said external power source to an electric power for charging said main power storage device, at a time of external charging for charging said main power storage device by said external power source; a power control unit for controlling driving of an electric motor for generating vehicle driving power, by electric power conversion between said main power storage device and said electric motor; a first switch (SMR1, SMR2) connected between said main power storage device and said power control unit; a second switch (RL1, RL2) connected parallel to said first switch (SMR1, SMR2), between said charger and said main power storage device; a plurality of auxiliary loads (90, 95/81, 82, 95) formed to operate by the supply of electric power for auxiliary system from a power supply line connected to said sub power storage unit; a first voltage converter for converting an output voltage of said main power storage unit to a level of an output voltage of said sub power storage device and outputting to said power supply line; a second voltage converter, having an output capacity smaller than said first voltage converter, for converting an output voltage of said charger to the level of the output voltage of said sub power storage device and outputting to said power supply line; and a controller (80, 85), operated by electric power supplied from said sub power storage device, for controlling open/close of said first and second switches (SMR1, SMR2, RL1, RL2) as well as operation and stop of said first and second voltage converters (60, 115); wherein said controller (80, 85) is adapted such that at the start of said external charging, said first switch (SMR1, SMR2) is opened and said second switch (RL1, RL2) is closed, said first voltage converter is stopped and said second voltage converter is operated, and when the electric power for said auxiliary system is determined to be insufficient during execution of said external charging, said first voltage converter is operated, and that the first switch (SMR1, SMR2) is closed in addition to operating the first voltage converter, when the electric power for the auxiliary system is determined to be insufficient during execution of the external charging. rechargeable main power storage device and sub power storage device; a charger for converting electric power supplied from said external power source to an electric power for charging said main power storage device, at a time of external charging for charging said main power storage device by said external power source; a power control unit for controlling driving of an electric motor for generating vehicle driving power, by electric power conversion between said main power storage device and said electric motor; a first switch (SMR1, SMR2) connected between said main power storage device and said power control unit; a second switch (RL1, RL2) connected parallel to said first switch (SMR1, SMR2), between said charger and said main power storage device; a plurality of auxiliary loads (90, 95/81, 82, 95) formed to operate by the supply of electric power for auxiliary system from a power supply line connected to said sub power storage unit; a first voltage converter for converting an output voltage of said main power storage unit to a level of an output voltage of said sub power storage device and outputting to said power supply line; a second voltage converter, having an output capacity smaller than said first voltage converter, for converting an output voltage of said charger to the level of the output voltage of said sub power storage device and outputting to said power supply line; and a controller (80, 85), operated by electric power supplied from said sub power storage device, for controlling open/close of said first and second switches (SMR1, SMR2, RL1, RL2) as well as operation and stop of said first and second voltage converters (60, 115); wherein said controller (80, 85) is adapted such that at the start of said external charging, said first switch (SMR1, SMR2) is opened and said second switch (RL1, RL2) is closed, said first voltage converter is stopped and said second voltage converter is operated, and when the electric power for said auxiliary system is determined to be insufficient during execution of said external charging, said first voltage converter is operated, and that the first switch (SMR1, SMR2) is closed in addition to operating the first voltage converter, when the electric power for the auxiliary system is determined to be insufficient during execution of the external charging.