A specific environmental stress on vegetation is calculated highly accurately and relatively easily. For generation of environmental stress information, vegetation information is obtained first using an imaging signal of vegetation. Furthermore, reference vegetation information associated with vegetation information in a state of being free of, for example, a specific environmental stress is obtained. Moreover, as information associated with an environmental stress on the vegetation, difference information between vegetation information acquired from an imaging signal of vegetation in a state of being likely to have the specific environmental stress and the reference vegetation information is obtained.
