PURPOSE: To provide an electric "Kotatsu" of which heating efficiency is high, which is convenient for moving and for housing in place, and is to be usable for multi-purpose table, by increasing the inside space surrounded by a framework, by providing a folding extensible part to each side of a rectangular main body in which a built-in electric heater is provided as a heating means.

CONSTITUTION: An electric heater can be moved and can be housed in place by folding extensible parts 1b to the side of the surface or the backside of a main body 1a, or in the state that the parts 1b are extended in a flat table. Four feet 7 are respectively put into the cutout parts 9 of a main body 1, and are locked in frame pieces 6a by jointing parts 8 and 8' with an arbitrary extensible part (s) 1b left folded according to the necessity. At this time, the extensible part 1b on a side from which a person puts his feet into a Kotatsu is left open not to be folded, and a quilt is covered over a framework to keep warmth in it. With such an arrangement the necessary extensible part 1b for sitting only is open, so that portability of the heater and housing space for it are facilitated, as well as to prevent heat from dissipating from a heated space.