A variable shape frame, comprising: a plurality of extendable arms (A,B,C,D) arranged to form a frame; and a coupling mechanism that couples ends of adjoining ones of said extendable arms so that said adjoining extendable arms can move together, wherein each of said extendable arms includes a plurality of cross units each formed by two rigid members (21,22) crossing each other in an X-shape and pivotally coupled by a middle coupling shaft, and an end coupling portion pivotally coupling ends of adjoining ones of said cross units, said end coupling portion includes inner end coupling shafts located on an inner side, and outer end coupling shafts located on an outer side, characterised in that each of said rigid members has a curved shape so that said extendable arm extends and contracts along a curved track, and said coupling mechanism includes first bent members each pivotally coupling said inner end coupling shaft of one of adjoining two of said extendable arms and said outer end coupling shaft of the other extendable arm, second bent members each pivotally coupling said outer end coupling shaft of said one of adjoining two of said extendable arms and said inner end coupling shaft of the other extendable arm, and bent portion coupling shafts each pivotally coupling said first bent member and said second bent member at an intersection of said first and second bent members, such that the area of the variable shape frame changes with the extension of the extendable arms. a plurality of extendable arms (A,B,C,D) arranged to form a frame; and a coupling mechanism that couples ends of adjoining ones of said extendable arms so that said adjoining extendable arms can move together, wherein each of said extendable arms includes a plurality of cross units each formed by two rigid members (21,22) crossing each other in an X-shape and pivotally coupled by a middle coupling shaft, and an end coupling portion pivotally coupling ends of adjoining ones of said cross units, said end coupling portion includes inner end coupling shafts located on an inner side, and outer end coupling shafts located on an outer side, characterised in that each of said rigid members has a curved shape so that said extendable arm extends and contracts along a curved track, and said coupling mechanism includes first bent members each pivotally coupling said inner end coupling shaft of one of adjoining two of said extendable arms and said outer end coupling shaft of the other extendable arm, second bent members each pivotally coupling said outer end coupling shaft of said one of adjoining two of said extendable arms and said inner end coupling shaft of the other extendable arm, and bent portion coupling shafts each pivotally coupling said first bent member and said second bent member at an intersection of said first and second bent members, such that the area of the variable shape frame changes with the extension of the extendable arms. first bent members each pivotally coupling said inner end coupling shaft of one of adjoining two of said extendable arms and said outer end coupling shaft of the other extendable arm, second bent members each pivotally coupling said outer end coupling shaft of said one of adjoining two of said extendable arms and said inner end coupling shaft of the other extendable arm, and bent portion coupling shafts each pivotally coupling said first bent member and said second bent member at an intersection of said first and second bent members, such that the area of the variable shape frame changes with the extension of the extendable arms.