<p>Disclosed is a method for detecting cancer cells in a blood sample. The method comprises the steps of: incubating a blood sample that is suspected to contain cancer cells together with an oncolytic virus to cause the oncolytic virus to be proliferated in at least the cancer cells; mixing the blood sample that has been treated in the preceding proliferation step with an immobilizing agent and a nonionic surfactant; and detecting cancer cells which are contained in the blood sample obtained by the aforementioned mixing step and in which the oncolytic virus has been proliferated.</p>
