A vehicle power supply device configured to supply electric power to a load, the vehicle power supply device comprising: a capacitor unit configured to supply the electric power to the load, the capacitor unit including a plurality of capacitors storing auxiliary power; a temperature sensor detecting a temperature of the capacitor unit; a charge circuit charging electric power to the capacitor unit; a capacitor-unit current detector detecting a current value of the capacitor unit; a capacitor-unit voltage detector detecting a voltage value of the capacitor unit; a controller electrically connected to the temperature sensor, the charge circuit, the capacitor-unit current detector, and the capacitor-unit voltage detector, the controller obtaining an internal resistance value and a capacitance value of the capacitor unit from the voltage value and the current value; a storage storing a correction calculation formula being used to perform the correction calculation of the internal resistance value and the capacitance value in accordance with the temperature in order to obtain a corrected calculated value of internal resistance and a corrected calculated value of capacitance (Ccal); and a determination unit determining a degradation level of the capacitor unit, characterized in that the storage further stores a plurality of degradation determination formulas different from each other, each of the plurality of degradation determination formulas corresponding to respective one of numerical ranges of the corrected calculated value of capacitance, the plurality of degradation determination formulas being merged to form a degradation determination line comprising plural values of an internal resistance standard value (Rstd) so as to maximize the capacitance value of the capacitor unit and to minimize the internal resistance value of the capacitor unit in the respective one of numerical ranges of the corrected calculated value of capacitance (Ccal), the controller calculates the plural values of the internal resistance standard value (Rstd) each corresponding to respective one of numerical ranges of the corrected calculated value of capacitance (Ccal) when the capacitor unit supplies electric power intermittently to the load, and the determination unit determines the degradation level of the capacitor unit based on at least the plural values of the internal resistance standard value (Rstd) on the degradation determination line in comparison with a calculated resistance value (Rcal) or the corrected calculated value of capacitance (Ccal) in comparison with a capacitance degradation value (Clim). a capacitor unit configured to supply the electric power to the load, the capacitor unit including a plurality of capacitors storing auxiliary power; a temperature sensor detecting a temperature of the capacitor unit; a charge circuit charging electric power to the capacitor unit; a capacitor-unit current detector detecting a current value of the capacitor unit; a capacitor-unit voltage detector detecting a voltage value of the capacitor unit; a controller electrically connected to the temperature sensor, the charge circuit, the capacitor-unit current detector, and the capacitor-unit voltage detector, the controller obtaining an internal resistance value and a capacitance value of the capacitor unit from the voltage value and the current value; a storage storing a correction calculation formula being used to perform the correction calculation of the internal resistance value and the capacitance value in accordance with the temperature in order to obtain a corrected calculated value of internal resistance and a corrected calculated value of capacitance (Ccal); and a determination unit determining a degradation level of the capacitor unit, characterized in that the storage further stores a plurality of degradation determination formulas different from each other, each of the plurality of degradation determination formulas corresponding to respective one of numerical ranges of the corrected calculated value of capacitance, the plurality of degradation determination formulas being merged to form a degradation determination line comprising plural values of an internal resistance standard value (Rstd) so as to maximize the capacitance value of the capacitor unit and to minimize the internal resistance value of the capacitor unit in the respective one of numerical ranges of the corrected calculated value of capacitance (Ccal), the controller calculates the plural values of the internal resistance standard value (Rstd) each corresponding to respective one of numerical ranges of the corrected calculated value of capacitance (Ccal) when the capacitor unit supplies electric power intermittently to the load, and the determination unit determines the degradation level of the capacitor unit based on at least the plural values of the internal resistance standard value (Rstd) on the degradation determination line in comparison with a calculated resistance value (Rcal) or the corrected calculated value of capacitance (Ccal) in comparison with a capacitance degradation value (Clim).