The present invention addresses the problem of providing an improved negative-strand RNA viral vector enabling transient high expression of a gene carried by the vector, and quick removal of the vector after the expression, and the use thereof. It was found that if a degron is added to a P-protein possessed by a negative-strand RNA viral vector, high-level expression of a gene carried by the vector is transiently induced after introduction of the vector, and thereafter, the vector can be quickly removed in a manner dependent on the degron. In particular, if the degron is added to a temperature-sensitive P-protein, the vector can be removed to a level below the detection limit within two weeks after cells are infected with the vector. Since the present invention is useful for transiently expressing a transcription factor, such as a reprogramming factor or the like, in target cells, and then quickly removing the vector, the present invention is expected to be applied in cell therapy and regenerative medicine.