The present invention provides a therapeutic agent for psoriasis or atopic dermatitis, and comprises anti-Staphylococcus aureus antibodies as the active ingredient. A therapeutic agent for psoriasis or atopic dermatitis is specifically provided. This agent comprises comprehensive anti-S. aureus surface antibodies, including antibodies against entire cell-surface proteins, as the active ingredient. The agent is obtainable by: (a) treating S. aureus with a protein crosslinking/fixation reagent to fix proteins expressed on the surface of S. aureus via intramolecular crosslinking; (b) administering S. aureus treated with the protein crosslinking/fixation reagent for protein fixation to an animal as an immunogen; and (c) obtaining an antibody from the animal.