Provided is a pharmaceutical agent for effective prophylaxis and/or treatment of a pathological condition with decreased lung compliance. The pharmaceutical agent for prophylaxis and/or treatment of a pathological condition with decreased lung compliance is characterized by having a polyamine. The polyamine includes at least one of spermine (Spm), spermidine (Spd), and putrescine (Put). The pharmaceutical agent improves lung compliance and ameliorates gas exchange dysfunction, and therefore, can ameliorate pathological conditions such as acute respiratory distress syndrome (ARDS), acute lung injury (ALI), lung diseases caused by dysfunctional endogenous pulmonary alveolar surfactant, multiple organ dysfunction syndrome (MODS), and cardiogenic pulmonary edema.