the present invention relates to biodegradable plastics and biodegradable plastic products thereof having flexibility , and more specifically , it aims to provide a plasticizer for providing aliphatic polyester , in particular , polylactic acid with flexibility , an aliphatic polyester composition using the same , a film , a sheet , a bag and the like obtained by molding said composition , that are , with respect to 100 parts by weight of aliphatic polyester , an aliphatic polyester compound which contains polyglycerol acetic ester by 5 - 50 parts by weight , an aliphatic polyester compound which contains polyglycerol acetic ester and acetic and fatty acid ester of glycerol having a specific structure by 5 - 50 parts by weight , and flexible products which are obtained by molding the fatty polyester compound indicated in the above or into films , sheets , bags or the like .