The present invention provides a transgenic non-human mammal retaining, in a specifically expressible state, a DNA encoding IL-33 in the skin, and having one or more features selected from the group consisting of (1) spontaneous onset of dermatitis, (2) increase in the number of inflammatory cells, (3) increase in total IgE concentration, histamine concentration, cytokine concentration and/or chemokine concentration, and (4) increase in scratching time, under SPF (specific pathogen free) breeding conditions, as compared to a corresponding non-transgenic non-human mammal, and the like.