The present invention addresses the problem of providing a sustained-release injectable formulation for releasing a therapeutically effective amount of 7-[4-(4-benzo[b]thiophene-4-yl-piperazine-1-yl)butoxy]-1H-quinoline-2-one in at least one week, as a long-acting form of drug administration for 7-[4-(4-benzo[b]thiophene-4-yl-piperazine-1-yl)butoxy]-1H-quinoline-2-one. The present invention provides an injectable formulation the concentration of which in the blood can be sustained for at least one week, the formulation comprising 7-[4-(4-benzo[b]thiophene-4-yl-piperazine-1-yl)butoxy]-1H-quinoline-2-one or a salt thereof as an active ingredient.
