It is an object to provide a combination therapy effective in cancer immunotherapy. The object is achieved by providing an anti-tumor agent, including a transformed Bifidobacterium containing DNA encoding a WT1 protein and DNA encoding a GNB/LNB substrate-binding membrane protein derived from a Bifidobacterium, the transformed Bifidobacterium being designed to display the WT1 protein as an antigen on a surface of the transformed Bifidobacterium, the anti-tumor agent being for use in combination with an immunosuppression inhibitor. The transformed Bifidobacterium can be used as an oral tumor vaccine.