The main purpose of the present invention is to provide a novel antiviral agent having a useful pharmacological action. The present inventors found that the above-described purpose can be achieved by a complex in which two synthetic RNAs (e.g., poly-I and poly-C) that can together form a double strand are contained in a drug carrier useful for transporting a drug into a cell (e.g., cationic liposome and atelocollagen), and thus the present invention was achieved.