A structure, which has both a drug holding capability and a sustained release ability utilizing a liposome and mechanical strength of a polyhydroxyalkanoate. This structure is excellent in holding capability for hydrophilic drugs and other water-soluble substances, as well as lipophilic drugs and other hydrophobic substances, and is capable of controlling the sustained release ability. The polyhydroxyalkanoate coats at least a part of the outer wall of the liposome.