An object of the present invention is to provide a conditionally replicating adenovirus having a strong anticancer effect. A conditionally replicating adenovirus to replicate specifically in a cancer cell and express REIC protein or REIC C domain protein, wherein the conditionally replicating adenovirus is obtained by inserting full-length REIC DNA or REIC C domain DNA into a conditionally replicating adenovirus comprising an ITR (inverted terminal repeat) sequence of an adenovirus type 5 genome and insertion of an HRE sequence, an hTERT promoter, a decorin-encoding DNA, and a DNA encoding a peptide comprising an RGD sequence.