To provide an elastase inhibitor which exhibits a high elastase-inhibiting action even in a small amount.

This elastase inhibitor comprises a hydrolysable N-acylated derivative salt represented by the general formula (1) [RCO is a 8 to 18C straight chain or branched chain saturated or unsaturated fatty acid residue; R1 is an amino acid side chain constituting a protein; (n) is 3 to 30; M is a monovalent or divalent metal atom (therein, 1/2 equivalent in the case of the divalent metal atom), NH4 or an organic amine compound onium]. The hydrolysable protein has especially preferably an amino acid polymerization degree of 3 to 10. A protein source is preferably collagen, silk, casein, soybean protein or pea protein.