The present invention addresses the problem of providing a prophylactic/therapeutic agent which is inexpensive, has little adverse side effects and is effective against persistent virus infections. A 5-aminolevulinic acid compound represented by the following formula (I) (wherein R1 represents a hydrogen atom or an acyl group； and R2 represents a hydrogen atom, a linear or branched alkyl group, a cycloalkyl group, an aryl group or an aralkyl group) or a salt thereof can be used as a prophylactic and/or therapeutic agent for virus infections to prevent proliferation of viruses.
