A power storage system (100, 100A), comprising: a power generation element configured to perform environmental power generation; a first storage battery configured to receive power generated by the power generation element and supply the power to a load device (200, 200A); a second storage battery configured to have a capacitance smaller than that of the first storage battery and to be connected in series with the first storage battery; a first switcher configured to be connected in parallel to the second storage battery, short-circuits both terminals of the second storage battery in a closed state, and releases a short-circuited state of the second storage battery in an open state; and a switching unit (150, 150A) configured to control the opened and closed states of the first switcher, wherein the switching unit (150, 150A) when both terminals of the second storage battery are short-circuited by the first switcher and the load device (200, 200A) is charged from the first storage battery via the first switcher, compares a charging voltage of the first storage battery with a predetermined first threshold voltage, and performs control so that the first switcher enters an open state when the charging voltage of the first storage battery becomes equal to or lower than the predetermined first threshold voltage, determines the charging voltage of the entire series circuit of the first storage battery and the second storage battery or determines the charging voltage of a single entity of the second storage battery and sums the determined charging voltage and the charging voltage of the first storage battery to obtain the charging voltage of the entire series circuit when the short-circuited state of both terminals of the second storage battery is released by the first switcher and the series circuit is charged from the power generation element, and performs control so that the first switcher enters the closed state when the charging voltage of the entire series circuit becomes equal to or higher than a predetermined second threshold voltage that is higher than the first threshold voltage. a power generation element configured to perform environmental power generation; a first storage battery configured to receive power generated by the power generation element and supply the power to a load device (200, 200A); a second storage battery configured to have a capacitance smaller than that of the first storage battery and to be connected in series with the first storage battery; a first switcher configured to be connected in parallel to the second storage battery, short-circuits both terminals of the second storage battery in a closed state, and releases a short-circuited state of the second storage battery in an open state; and a switching unit (150, 150A) configured to control the opened and closed states of the first switcher, wherein the switching unit (150, 150A) when both terminals of the second storage battery are short-circuited by the first switcher and the load device (200, 200A) is charged from the first storage battery via the first switcher, compares a charging voltage of the first storage battery with a predetermined first threshold voltage, and performs control so that the first switcher enters an open state when the charging voltage of the first storage battery becomes equal to or lower than the predetermined first threshold voltage, determines the charging voltage of the entire series circuit of the first storage battery and the second storage battery or determines the charging voltage of a single entity of the second storage battery and sums the determined charging voltage and the charging voltage of the first storage battery to obtain the charging voltage of the entire series circuit when the short-circuited state of both terminals of the second storage battery is released by the first switcher and the series circuit is charged from the power generation element, and performs control so that the first switcher enters the closed state when the charging voltage of the entire series circuit becomes equal to or higher than a predetermined second threshold voltage that is higher than the first threshold voltage.