To provide a portable knockdown chair with extremely reduced size.

A chair 10 includes lower frames 12, upper frames 14, a seat portion 16, and a belt 18, and has two postures of an unfolded state for use and a disassembled and folded state for carrying. The lower frames 12 are separated from the upper frames 14. The lower frames 12 and the upper frames 14 are flattened by aligning the phases of the inside and outside pipe members.