The inventors of the present invention found that an HMGB1 peptide fragment having a specific amino acid sequence is effective at suppressing finger fusion and scarring of the digestive tract, and at prolonging survival in malnutrition- type epidermolysis bullosa model mice. The inventors also found that in a cutaneous ulcer model, administration of the specific HMGB1 peptide fragment suppresses the fibrosing of skin that occurs in the healing process of the ulcer. The present invention, on the basis of these findings, provides a pharmaceutical composition for fibrous disease treatment, which contains the specific HMGB1 peptide fragment.
