The invention provides a pocketable body warmer for conducting heat of a heater in high efficiency to a surface integer of a case, which reduces heat conduction to a cell housed in the case and prevents severe effect caused by the heat conducted to the cell. The pocketable body warmer includes: a metallic exterior casing with a metal plate being formed to a tube having a closed bottom end and an open opposite end a plastic-made interior casing with an outer contour being formed to be inserted in the metallic exterior casing, the interior casing being provided with a battery storage portion a battery loaded in the interior casing and a heater thermally connected to the metallic exterior casing for heating the metallic exterior casing.
