It is intended to provide a natural biodegradable material having both properties of biodegradability and mechanical strength; a biodegradable film or container produced from the natural biodegradable material; a binder for producing the biodegradable material; and a method for producing these. A natural polymeric substance which has a cellulose-like property of having hydroxy group which is not present in a petroleum-derived polymeric compound, and which moreover has a polypropylene-like structure is obtained by the steps of using a cereal starch such as Kaoliang starch as a culture raw material, adding a microorganism belonging to the genus Bacillus to the raw material to conduct a culture, and recovering a viscous polymeric substance. A biodegradable material having biodegradability comparable to that of cellulose and also having a mechanical strength property of polypropylene can be obtained by using the natural polymeric substance as a binder and mixing starch and/or shell powder thereto. A film or container produced by using this biodegradable material has superior properties in both biodegradability and mechanical strength.