1. A method for determining the order in which a specimen is scanned in a scanning electron microscope in which the specimen is irradiated with a primary electron beam to acquire an image of the specimen, the method comprising: the time constant extraction step of controlling time constant extraction means to extract the time constant of a temporal change curve indicative of the relationship of the signal magnitude of the electrons caught by an energy filter for catching electrons having at least a predetermined energy level among the electrons emitted from the specimen with the electron beam irradiation time; and the scanning order determination step of controlling scanning order determination means to determine the scanning order in which the electron beam scans the specimen based on the extracted time constant.