It is a futon to lay under the body. It is defined as a futon to lay under the body when sleeping” by the JIS. In Japan, a mattress and a shiki-buton aren’t the same thing. A shiki-buton can be used as follows. ①A shiki-buton can be laid directly on the tatami-mat floor.②After placing mattress directly on the wooden floor, a shiki-buton can be laid on it. ③A shiki-buton can be used on the mattress of the bed. Also, some people lay a highly functional mattress instead of a shiki-buton and sleep on it.