A recovery device is configured to recover specific material as a dewatering aid from sludge generated in a sewage treatment process. The recovery device includes: a grinder configured to fragment a solid in the sludge to obtain prepared sludge; a separator configured to separate hardly decomposable organic matter and easily decomposable organic matter from the prepared sludge; and an extractor configured to continuously extract hardly decomposable organic matter having specific properties as the dewatering aid from the hardly decomposable organic matter separated by the separator.