Abstract: A detecting device is provided, which collocates with an electronic device to constitute a diagnostic system. The detecting device comprises a main-body, a carrier, an image sensor, a controller and a transmission interface. The carrier is disposed within the main-body for carrying a specimen. The image sensor is disposed within the main-body for detecting the specimen and generating a sensor signal. The controller is electrically connected with the image sensor for processing the sensor signal into an image signal. The transmission interface is electrically connected with the controller and the image signal is transmitted to the electronic device via the transmission interface.