The present invention provides a 1,2,4-triazolone derivative represented by general formula (1A), which acts as an arginine vasopressin 1b receptor antagonist； a pharmacologically acceptable salt thereof； and a drug containing the same as an active ingredient, particularly a therapeutic or prophylactic agent exhibiting favorable in-vivo disposition in the case of mood disorders, anxiety disorders, schizophrenia, Alzheimer's disease, Parkinson's disease, Huntington's disease, eating disorders, hypertension, gastrointestinal disorders, drug dependency, epilepsy, cerebral infarction, cerebral ischemia, cerebral edema, head trauma, inflammation, immunological disorders, hair loss, and other diseases.
