PURPOSE: To prevent the user of an electric KOTATSU from forgetting to turn OFF the electric KOTATSU, by a method wherein a collapsible seat is provided with an inlet plug socket, a switch to be turned ON and OFF by a load and an outlet plug socket, and an electric KOTATSU is connected to the outlet plug socket.

CONSTITUTION: The switch 2 which is closed when a predetermined load is exerted thereon is provided at a part of the collapsible seat 4 where the hips of a person taking the seat 4 are seated, and it is connected between the inlet plug socket 1 and the outlet plug socket 3 which are also provided in the seat 4. A power source is connected to the inlet plug socket 1, and the electric KOTATSU is connected to the outlet plug socket 3.