To provide a herpes virus in which a non-essential gene for replication is inactivated and a therapeutic agent using the same.

The herpes virus (preferably the herpes simplex virus, and more preferably herpes simplex virus 1 or herpes simplex virus 2) in which a non-essential gene for replication is inactivated contains US3 or UL56 gene present in a UL or US region. The method, the composition and the use for treating various diseases or disorders including tumor and infectious diseases comprise using the virus. The method, the composition and the use for activating a prodrug are provided.