It is intended to provide a method of detecting brain tumor whereby brain tumor can be surely detected at the early stage a brain tumor-detecting agent to be used therein and a medicinal composition for treating brain tumor. Detection of brain tumor based on the detection of an N-binding sugar chain A2G2F of a glycoprotein, which is specifically expressed in brain tumor, contributes to the early detection and treatment for brain tumor. Moreover, brain tumor can be surely detected at the early stage by using a lectin capable of binding specifically to the N-binding sugar chain A2G2F. A brain tumor-detecting agent having the lectin capable of binding specifically to the N-binding sugar chain A2G2F of the glycoprotein makes it possible to early an deasily detect brain tumor based on the sugar chain A2G2F. A medicinal composition containing as the active ingredient the lectin capable of binding specifically to the N-binding sugar chain A2G2F of the glycoprotein induces apoptosis in brain tumor cells and, therefore, is efficacious in preventing and treating diseases caused by brain tumor cells.
