To allow users ranging from infants and schoolchildren to junior and senior high school students or adults including college students to use a bed over a long period by freely varying the bed length and to convert the bed into a chair when the bed is not required.

A head side bed frame 2 and a foot side bed frame 3 are interconnected to achieve a desired bed frame length, and floor panels 4, 5, 6 are provided inside the bed frames 2, 3 so that a bed of the,desired length can be formed. The bed is disassembled and the floor panels 4, 5, 6 are provided inside the head side bed frame 2 or foot side bed frame 3 so that a chair can be formed.