Provided are a battery system and temperature control method therefor capable of suppressing excessive cooling of a battery module, diminishing a temperature variance, and leveling the temperatures of plural battery modules. In the battery system including cooling units each of which is provided with a cooling plate (2-1, 2-2) which includes a flow channel through which a refrigerant flows and on which a battery module that is an object of temperature control (1M-1, 1M-2) is placed, and a flow rate adjustment device (8-1, 8-2) that adjusts the flow rate of the refrigerant that flows through the flow channel, temperature sensors (6-1, 6-2) that individually sense the temperatures of the battery modules, and a refrigerant circulation mechanism (4) that branches out the refrigerant into the flow channels accompanying the cooling units, and joins and circulates the refrigerants coming from the flow channels, a control unit (7) adjusts the refrigerant flow rates using the flow rate adjustment devices (8-1, 8-2) according to the temperatures, which are sensed by the temperature sensors (6-1, 6-2), for each of the cooling units.