1. A scanning electron microscope in which a specimen is irradiated with a primary electron beam to acquire an image of the specimen, the scanning electron microscope comprising: a deflector, which scans the specimen with the primary electron beam: an energy filter, which selectively permits electrons having more than a predetermined energy level among the electrons emitted from the specimen to pass; a detector, which outputs a detection signal based on the electrons that have passed through the energy filter; and a scanning order determination device, which determines a scanning order of a scanning line of the deflector, the scanning order being determined in response to a temporal change of an intensity of the detection signal outputted from the detector.