To provide a therapeutic agent for retrovirus infection that comprises concentrated filtrate from a culture solution prepared by cocultivation of a plurality of beneficial microorganisms selected from yeast fungi and lactic acid bacteria in a specific combination.

The therapeutic agent for infections caused by retrovirus, particularly acquired immunodeficiency syndrome (AIDS) or adult T cell leukemia (ATL) reinforces congenital immune response in a living body to secrete living body antimicrobial peptide, e.g., defensin or the like whereby antiviral action is developed.