Provided is a binder for an electrostatic image developing toner using a polyester resin in which at least a part of a carboxylic acid component (a) and/or an alcohol component (b) comprises a carboxy-modified polyolefin or a hydroxyl-terminated polyalkadiene that may be hydrogenated containing an aliphatic hydrocarbon group (x) having a carbon number of 100 to 1,000. The binder is excellent in environmental stability and does not generate a peculiar odor around a copier or a printer when the binder is used in a toner, and a toner using the binder.