A detecting apparatus for detecting operation of a fan, includes a first current module disposed at an airflow path of the fan, a second current module insulated from the airflow, and an indicating module for giving an indicating signal, having a LED, and a transistor. The first and second current modules being mirror-images of each other. When the fan does not operate, the first and second current modules operate the same. The transistor of the indicating module is turned off, and the LED to be lit. When the fan operates, current flow of the first and second modules are different from each other producing a voltage greater than zero, the transistor of the indicating module is turned on, and the LED does not light.