The present invention addresses the problem of providing a substance that has an effect of increasing ATP in cells, in particular, an ATP increasing agent that has an effect much stronger than the increasing effect achieved by using inosine or febuxostat alone. An agent for increasing ATP in human or animal cells, said agent comprising a combination of A) with B): A) a xanthine oxidase/xanthine dehydrogenase inhibitor or a pharmaceutically acceptable salt thereof； and B) one or more compounds selected from among inosine, inosinic acid, hypoxanthine and pharmaceutically acceptable salts thereof.
