An extendable container including a container body and a sheet, the container body having a bottom part, a bellows barrel part extendable in a height direction, and a top part having an openable cover, the sheet being wrapped around the outer circumference of the container body to secure the container body, wherein the bellows barrel part includes ring portions, each having a predetermined width and trough portions, the ring portions including projections arranged thereon, and wherein the sheet includes locking holes at positions in alignment with the projections of the ring portion such that the locking holes receive the respective projections when the sheet is wrapped around the bellows barrel part.