Provided is an aqueous pharmaceutical preparation comprising 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one (compound (I)) or a salt thereof, which shows improved water solubility of compound (I) or a salt thereof achieved by addition of substituted &bgr；-cyclodextrin. The present invention provides a pharmaceutical preparation comprising compound (I) or a salt thereof, and substituted &bgr；-cyclodextrin.
