A nitrogen-containing bicyclic compound of formula (I) or a pharmaceutically acceptable salt thereof (wherein the symbols have the same meanings as described in the specification). ##STR00001## The compound of formula (I) has an inhibitory activity against PDE7 and it is useful for the prevention and/or treatment of various diseases, i.e. autoimmune diseases (ulcerative colitis, Crohn's disease, rheumatism, psoriasis, multiple sclerosis, collagenosis, etc.), inflammatory diseases (obstructive pulmonary disease, sepsis, pancreatitis, sarcoidosis, nephritis, hepatitis, enteritis, etc.), allergic diseases (asthma, allergic rhinitis, allergic conjunctivitis, seasonal conjunctivitis, atopic dermatitis, etc.), rejection of organ transplants, serious graft versus host disease (GVHD), diabetic disease, osteoporosis, bone fracture, restenosis, atherosclerosis, obesity, ischemic reperfusion injury, depression, Parkinson's disease, dementia, leukemia, etc.