A pocketable body warmer includes: a metallic exterior casing with a metal plate being formed in the shape of a tube having a closed bottom end and an open opposite end; and a plastic interior casing with an outer contour being formed to be inserted in the metallic exterior casing. The interior casing is provided with a battery storage portion and a battery is loaded in the battery storage portion. Also, a heater is thermally connected to the metallic exterior casing for heating the metallic exterior casing.