The present invention provides a 1,2,4-triazolone derivative represented by Formula (1A) having an antagonistic activity on the arginine-vasopressin 1b receptor or a pharmaceutically acceptable salt thereof and provides a pharmaceutical composition comprising the compound or the salt as an active ingredient, in particular, a therapeutic or preventive agent exhibiting favorable pharmacokinetics in a disease such as mood disorder, anxiety disorder, schizophrenia, Alzheimer's disease, Parkinson's disease, Huntington's chorea, eating disorder, hypertension, gastrointestinal disease, drug addiction, epilepsy, cerebral infarction, cerebral ischemia, cerebral edema, head injury, inflammation, immune-related disease, or alopecia.
