NOVELTY - The device has a battery holder (40) that accommodates a cylindrical battery. The battery holder is provided with a thermal radiation wall in alignment with a side surface of a portion of the cylindrical battery. A holding wall is provided to clamp the cylindrical battery through the thermal radiation wall. The thermal radiation wall is formed to be thinner than the holding wall while contacting thermally with the cylindrical batteries. The roughening process of the surface facing the cylindrical battery is carried out.    USE - Power supply device for driving electric motor drive in electric vehicle such as hybrid car and for driving starter motor and air-conditioner.    ADVANTAGE - Since the thermal radiation wall formed along a cylindrical battery is provided with uniform and reduced thickness than the thickness of the holding wall, the resistance of thermal radiation wall is suppressed so as to cool the cylindrical battery by transferring heat at the side of a thermal radiation wall and the surface area of the portion exposed to the surface of the battery holder is increased. Thus, the cooling efficiency can be improved without providing an air path in a battery holder and while maintaining the cylindrical battery with the battery holder. Since the reinforcing wall is provided adjacent to a thermal radiation wall, the cooling efficiency of the cylindrical battery is improved and the strength of a battery holder is maintained by suppressing the fall of physical strength of the radiation case. Since the effect of the adhesiveness of the thermal radiation wall and the cylindrical battery is improved, the cooling efficiency can be improved effectively. Since the external shape can be made into a rectangular parallelepiped shape, the device can be handled favorably. Since the power supply device connects the lead battery and the cylindrical battery in parallel, the effect of the electric current load of a lead battery is reduced.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the power supply device.(Drawing includes non-English language text)    Battery holder (40)    Holding case (50)    Radiation case (60)    Upper case (70)    Lower case (80)