A power storage system (100, 101, 101A, 102, 103) comprising: a power generation element that performs environmental power generation; a storage battery (120, 123) that is supplied with power generated by the power generation element; a DC/DC converter that converts an output voltage from the power generation element into a predetermined voltage; a first switch unit that switches whether to directly supply the output voltage from the power generation element to the storage battery (120, 123) or to supply thereto via the DC/DC converter; and a first changeover unit that compares a voltage of the storage battery (120, 123) with a first threshold voltage (Vc), and controls the first switch unit according to a comparison result, in a case where the first threshold voltage (Vc) is a predetermined voltage which is equal to or higher than a voltage (Vm) of the storage battery (120, 123) bringing the DC/DC converter into a main boost mode, wherein the first changeover unit controls the first switch unit so that the output voltage is directly supplied from the power generation element to the storage battery (120, 123), in a case where the voltage of the storage battery (120, 123) is equal to or lower than the first threshold voltage (Vc), and the first changeover unit controls the first switch unit so that the output voltage is supplied from the power generation element to the storage battery (120, 123) via the DC/DC converter, in a case where the voltage of the storage battery (120, 123) exceeds the first threshold voltage (Vc), characterized in that: the storage battery (120, 123) is constituted of a first storage battery and a second storage battery having a capacity larger than a capacity of the first storage battery, and in a case where a second threshold voltage is higher than the first threshold voltage (Vc), the output voltage is supplied to only the first storage battery from the power generation element if the voltage of the first storage battery is equal to or lower than the second threshold voltage. a power generation element that performs environmental power generation; a storage battery (120, 123) that is supplied with power generated by the power generation element; a DC/DC converter that converts an output voltage from the power generation element into a predetermined voltage; a first switch unit that switches whether to directly supply the output voltage from the power generation element to the storage battery (120, 123) or to supply thereto via the DC/DC converter; and a first changeover unit that compares a voltage of the storage battery (120, 123) with a first threshold voltage (Vc), and controls the first switch unit according to a comparison result, in a case where the first threshold voltage (Vc) is a predetermined voltage which is equal to or higher than a voltage (Vm) of the storage battery (120, 123) bringing the DC/DC converter into a main boost mode, wherein the first changeover unit controls the first switch unit so that the output voltage is directly supplied from the power generation element to the storage battery (120, 123), in a case where the voltage of the storage battery (120, 123) is equal to or lower than the first threshold voltage (Vc), and the first changeover unit controls the first switch unit so that the output voltage is supplied from the power generation element to the storage battery (120, 123) via the DC/DC converter, in a case where the voltage of the storage battery (120, 123) exceeds the first threshold voltage (Vc), characterized in that: the storage battery (120, 123) is constituted of a first storage battery and a second storage battery having a capacity larger than a capacity of the first storage battery, and in a case where a second threshold voltage is higher than the first threshold voltage (Vc), the output voltage is supplied to only the first storage battery from the power generation element if the voltage of the first storage battery is equal to or lower than the second threshold voltage. the storage battery (120, 123) is constituted of a first storage battery and a second storage battery having a capacity larger than a capacity of the first storage battery, and in a case where a second threshold voltage is higher than the first threshold voltage (Vc), the output voltage is supplied to only the first storage battery from the power generation element if the voltage of the first storage battery is equal to or lower than the second threshold voltage.