Delivery proteins are provided for transferring a protein, antibody or foreign substance into a cell without impairing the function or structure thereof. Further, methods of transferring a foreign substance into a cell at a high efficiency by using the delivery protein or an envelope virus or inactivated envelope virus in combination with said delivery protein are provided. The inventors discovered that a protein containing a polypeptide having an affinity for a constituent of the envelope virus contributes to the efficient enclosure of the foreign substance in the envelope. Moreover, the inventors discovered that use of the delivery protein enables foreign substances to be included in an envelope virus or inactivated envelope virus and therefore makes it possible to efficiently transfer the substances into cells without damaging the physiological function thereof.