An inspecting device for inspecting an inspection target is provided. The inspecting device includes a mono-color image-retrieving module, illuminating modules and a control module. The mono-color image-retrieving module is disposed above the inspection target with an optical axis orienting toward the inspection target. Each of the illuminating modules includes light-emitting elements of different colors. The control module controls the illuminating modules to sequentially generate illuminating lights both in an order of different colors and different incident angles to further control the mono-color image-retrieving module to sequentially retrieve mono-color images each in response to one illumination of the illuminating lights. The control module performs an inspection of the inspection target based on the mono-color images.