[Problem] To provide a compound useful as a cathepsin S inhibitor.[Solution] The present inventors have studied on a compound which has a cathepsin S-inhibiting activity and can be used as an active ingredient for a pharmaceutical composition for preventing and/or treating an autoimmune disease such as systemic lupus erythematosus (SLE) and lupus nephritis, an allergy, or organ, bone marrow or tissue graft rejection. As a result, it has been confirmed that a phenyldifluoromethyl-substituted prolineamide compound according to the present invention has a cathepsin S-inhibiting activity. This confirmation leads to the accomplishment of the present invention. The phenyldifluoromethyl-substituted prolineamide compound according to the present invention has a cathepsin S-inhibiting activity, and can be used as a prophylactic and/or therapeutic agent for an autoimmune disease such as SLE and nephritis, an allergy, or organ, bone marrow or tissue graft rejection.
