An intragastric balloon (1) to be placed in an inflated state in the stomach (S) is provided including: a balloon body that is made of an extensible material capable of being inflated and contracted； and a balloon medium that is enclosed in the balloon body and that includes a non-compressible volume holding material inflating the balloon body to hold a predetermined volume, wherein the total specific gravity of the balloon body and the balloon medium is less than that of water (the stomach contents S1).
