Abstract: The purpose of the present invention is to provide a method for highly accurately detecting a cancer cell. The method of the present invention is characterized by comprising imaging with the use of a fluorescently labeled L-glucose derivative. By using the method and imaging agent according to the present invention, a high contrast between a cancer cell and a normal cell can be obtained compared with the case that imaging is conducted with the use of a fluorescently labeled D-glucose derivative. According to this method, moreover, no fasting is needed for the determination. Thus, the imaging can be quickly carried out without imposing a burden on a patient.