An object of the present invention is to provide a sustained-release injectable preparation which is in a medication administration form that can provide the effect of 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one for a prolonged period of time, the preparation releasing a therapeutically effective amount of 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one for at least one week. The present invention provides an injectable preparation containing 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one or a salt thereof as an active ingredient, which releases the active ingredient in such a manner that its blood concentration is maintained for at least one week.
