The disclosure relates to 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 favourable in-vivo disposition in the case of mood disorders, anxiety disorders, schizophrenia, Alzheimer&rsquo；s disease, Parkinson&rsquo；s disease, Huntington&rsquo；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. Representative examples of 1,2,4-triazolone derivative are: 2-[3-(3-chlorophenyl)-1-{ 4-[2-(morpholin-4-yl)ethyl]phenyl} -5-oxo-1,5-dihydro-4H-1,2,4- triazol-4-yl]-N-(propan-2-yl)acetamide； 2-[3-(3-chlorophenyl)-1-{ 4-[2-(3-hydroxypyrrolidin-1-yl)ethyl]phenyl} -5-oxo-1,5-dihydro- 4H-1,2,4-triazol-4-yl]-N-(propan-2-yl)acetamide； 2-[3-(3-chlorophenyl)-1-(4-{ 2-[3-(hydroxymethyl)pyrrolidin-1-yl] ethyl} phenyl)-5-oxo-l,5- dihydro-4H-1,2,4-triazol-4-yl]-N-(propan-2-yl)acetamide； and 2-[3-(3-chlorophenyl)-1-{ 4-[2-(3-hydroxy-8-azabicyclo[3.2.1]oct-8-yl)ethyl]phenyl} -5-oxo- 1,5-dihydro-4H-1,2,4-triazol-4-yl]-N-(propan-2-yl)acetamide.
