The present invention relates to providing a reagent for cancer cell detection or cancer diagnosis, a pharmaceutical composition for the treatment of cancer, and a method of treating or preventing cancer in a subject. Specifically, the present invention relates to a reagent for cancer cell detection, comprising a recombinant virus where a replication cassette comprising a promoter from human telomerase, an E1A gene, an IRES sequence and an E1B gene in this order is integrated in E1 region of the viral genome and a labeling cassette comprising a gene encoding a labeling protein and a promoter capable of regulating the expression of the gene encoding the labeling protein is integrated in E3 region of the viral genome.