Protein crosslinking inhibitor and use thereof

Disclosed are: a ketone compound which is represented by general formula (1), (2) or (3) and has transglutaminase inhibitory activity; a protein crosslinking inhibitor which contains the compound; and a composition for prevention or treatment of diseases that are caused by crosslinking of proteins, said composition containing the compound or the protein crosslinking inhibitor. (In the formulae, R 1 represents a substituted or unsubstituted aryl group or heterocyclic group; R 2 , R 3 and R 4 each represents a hydrogen atom; n represents 2; X represents a halogen atom; and R 5 and R 6 each independently represents a hydrogen atom or a substituted or unsubstituted C 1 -C 10 alkyl group, aryl group or aralkyl group. In this connection, R 5 and R 6 are not hydrogen atoms at the same time, and R 5 and R 6 may combine together to form a saturated or unsaturated, substituted or unsubstituted heterocyclic group that contains a nitrogen atom (N).)