An optically active imidazolidinone derivative represented by general formula (1), having a cholinergic activity (a muscarine M.sub.1 activity) and being useful for treating senile dementia, a pharmacologically acceptable acid-addition salt thereof, and a process for producing the same, wherein R and R.sup.1 may be the same or different and each represents hydrogen, halogen, optionally halogenated lower alkyl, lower alkoxy, lower alkylthio, lower alkoxycarbonyl, nitro, amino or cyano; and n represents 1 to 4.