A power storage device comprising: a plurality of modules each including secondary batteries, a charging switch (SWc) that controls charging to the secondary batteries, a discharging switch (SWd) that controls discharging of the secondary batteries, and a voltage measuring unit (13, 17) that measures a voltage of the module; and a switch control unit that is configured to control one or both of the charging switch (SWc) and the discharging switch (SWd), wherein the modules are connected in parallel, wherein the switch control unit is configured to: maintain an on state of the discharging switch (SWd) for at least one of the modules for a predetermined period, control the charging switch (SWc) of the module in which a maximum module charging current estimated based on the voltage of the module is a predetermined value or less, to be in an on state, characterized in that the switch control unit is further configured to: select a first module in which the voltage of the module is the highest, among the plurality of modules, count the number of second modules in which a difference in module voltage from the first module is a certain value or less, among the plurality of modules, divide a system charging current by the number of second modules to obtain an estimated module charging current, and switch on the charging switches (SWc) of the first and second modules, when the estimated module charging current is smaller than a maximum charging current of the module. a plurality of modules each including secondary batteries, a charging switch (SWc) that controls charging to the secondary batteries, a discharging switch (SWd) that controls discharging of the secondary batteries, and a voltage measuring unit (13, 17) that measures a voltage of the module; and a switch control unit that is configured to control one or both of the charging switch (SWc) and the discharging switch (SWd), wherein the modules are connected in parallel, wherein the switch control unit is configured to: maintain an on state of the discharging switch (SWd) for at least one of the modules for a predetermined period, control the charging switch (SWc) of the module in which a maximum module charging current estimated based on the voltage of the module is a predetermined value or less, to be in an on state, maintain an on state of the discharging switch (SWd) for at least one of the modules for a predetermined period, control the charging switch (SWc) of the module in which a maximum module charging current estimated based on the voltage of the module is a predetermined value or less, to be in an on state, characterized in that the switch control unit is further configured to: select a first module in which the voltage of the module is the highest, among the plurality of modules, count the number of second modules in which a difference in module voltage from the first module is a certain value or less, among the plurality of modules, divide a system charging current by the number of second modules to obtain an estimated module charging current, and switch on the charging switches (SWc) of the first and second modules, when the estimated module charging current is smaller than a maximum charging current of the module. select a first module in which the voltage of the module is the highest, among the plurality of modules, count the number of second modules in which a difference in module voltage from the first module is a certain value or less, among the plurality of modules, divide a system charging current by the number of second modules to obtain an estimated module charging current, and switch on the charging switches (SWc) of the first and second modules, when the estimated module charging current is smaller than a maximum charging current of the module.