An appearance inspection device creates a combination of a first image which is a normal product image and a second image which is a product image as a comparison object, on the basis of a reference data set and a learning data set, and a machine learning device learns classification of a product corresponding to the second image as normal or not normal for the combination. The machine learning device observes the combination of the first image and the second image as a state variable representing a current state of an environment, acquires a label given to the second image as label data, and performs learning by associating the state variable with the label data.