The object of the present invention is to provide a novel conditionally replicating adenovirus and a reagent comprising the same for cancer cell detection or for cancer diagnosis.The present invention provides a polynucleotide, which comprises human telomerase reverse transcriptase (hTERT) promoter, E1A gene, IRES sequence and E1B gene in this order and which comprises a target sequence of a first miRNA. The present invention also provides a recombinant adenovirus, which comprises a replication cassette comprising the above polynucleotide, wherein the replication cassette is integrated into the E1 region of the adenovirus genome.