To use a futon for multipurpose throughout the year by adapting the size of the futon to that for a kotatsu when employed as a futon for a kotatsu used in a frame kotatsu or the like and splitting the futon so as to adapt to a mat for sleeping with clothes on, a leg sheet or a seat cushion for a car when not employed as a futon for a kotatsu.

The futon BC for a kotatsu such as a frame kotatsu is split into three multipurpose futon-like split structure bodies 1, 2 and 3 when two fastener means 4 and 5 are released and is used for kotatsu when two fastener means 4 and 5 are connected.