A biodegradable material is a chemically cross-linked product between a multivalent compound A having 3 or more functional groups X such as hydroxyl group and a multivalent compound B having 3 or more functional groups Y such as carboxyl group wherein chemical cross-linkage(s) is/are formed by condensation reaction of the functional group(s) X and the functional group(s) Y wherein (y+z)/(x+z) is 1.2 to 4.0 when MA>MB, and (x+z)/(y+z) is 1.2 to 4.0 when MA
