Battery temperature unevenness suppressing power supply

A power supply device is provided that includes a battery module 3 and a cooling mechanism. The battery module is composed of a plurality of batteries 20 arranged side by side. The cooling mechanism cools the batteries 20. A thermally-insulating member 70 is arranged on a part of a battery module surface, and thermally insulates heat generated from the batteries 3. This power supply device can reduce the temperature unevenness T.