Provided is a molten salt battery device and a temperature control method for a molten salt battery, which enable the molten salt battery temperature to be controlled at a uniform temperature and which also enable easy cooling. The molten salt battery device arranges a plurality of molten salt batteries (1) within a container (2) such that space is provided around the molten salt batteries (1), fills the space around the molten salt batteries (1) with a heat medium (3), and makes the heat medium (3) flow while controlling the temperature of the heat medium (3) with a temperature control unit (52) by the use of an electric heater (51). The molten salt battery device controls the temperature of the molten salt battery (1) by the heat exchange between the flowing heat medium (3) and the molten salt battery (1). The internal temperature of the molten salt battery (1) is controlled to a uniform temperature by the heat exchange with the heat medium (3) that surrounds the molten salt battery (1). The molten salt battery device can also easily cool the molten salt battery (1) by reducing the temperature of the heat medium (3).