An observation system includes a detector that detects light from a semiconductor device and outputs a detection signal, a 2D camera, an optical device that guides light to the detector and the 2D camera, an image processing unit that generates a first optical image of the semiconductor device based on the detection signal and receives an input of a first CAD image, an image analysis unit that learns a conversion process of the first CAD image by machine learning using the first optical image as training data, and converts the first CAD image into a second CAD image resembling the first optical image by the conversion process based on a result of the learning, and an alignment unit that performs alignment based on a second optical image and the second CAD image.