A power supply device comprising: a battery module , which includes three battery banks connected in series, each of which comprises a predetermined number of batteries connected in series; a negative electrode output terminal to which a negative electrode terminal of the battery module is connected; a positive electrode output terminal to which a positive electrode terminal of the battery module and a connection point between each of the battery banks are individually connectable through discharging switches (SW1, SW2, SW3); an output voltage detecting circuit configured to detect an output voltage between the positive electrode output terminal and the negative electrode output terminal ; a charging current adjusting circuit , which includes two charging switches (SW4 and SW5) and a current-limiting resistor (R1), configured to adjust a charging current of the battery module ; a plurality of state-of-charge detecting circuits configured to detect a state-of-charge of each of the battery banks of the battery module by detecting a temperature of each of the battery banks ; and a control device configured to control charge and discharge of the battery module , wherein the control device includes: means configured to control the discharging switches (SW1, SW2, SW3), so that the output voltage is within a specific range; and means configured to control the two charging switches (SW4, SW5) in the charging current adjusting circuit on the basis of the state-of-charge of each of the battery banks of the battery module . a battery module , which includes three battery banks connected in series, each of which comprises a predetermined number of batteries connected in series; a negative electrode output terminal to which a negative electrode terminal of the battery module is connected; a positive electrode output terminal to which a positive electrode terminal of the battery module and a connection point between each of the battery banks are individually connectable through discharging switches (SW1, SW2, SW3); an output voltage detecting circuit configured to detect an output voltage between the positive electrode output terminal and the negative electrode output terminal ; a charging current adjusting circuit , which includes two charging switches (SW4 and SW5) and a current-limiting resistor (R1), configured to adjust a charging current of the battery module ; a plurality of state-of-charge detecting circuits configured to detect a state-of-charge of each of the battery banks of the battery module by detecting a temperature of each of the battery banks ; and a control device configured to control charge and discharge of the battery module , wherein the control device includes: means configured to control the discharging switches (SW1, SW2, SW3), so that the output voltage is within a specific range; and means configured to control the two charging switches (SW4, SW5) in the charging current adjusting circuit on the basis of the state-of-charge of each of the battery banks of the battery module . means configured to control the discharging switches (SW1, SW2, SW3), so that the output voltage is within a specific range; and means configured to control the two charging switches (SW4, SW5) in the charging current adjusting circuit on the basis of the state-of-charge of each of the battery banks of the battery module . <EOS>