Provided is a sustained release preparation capable of uniformly releasing therefrom a volatile chemical for a long period of time even if the amount of a liquid chemical remaining in a tubular container of the sustained release preparation becomes small. Also provided is a container for sustained release preparation, the container being tubular and comprising two layers of outer and inner layers, the inner layer having a thickness of 0.12 to 1.2 mm and having a foamed structure permitting the soaking-up of a liquid chemical to a height of at least 25 mm by capillarity. Also provided is a container unit for sustained release preparation, the unit comprising two or more of the container combined.