The present application provides a human gene over-expressing animal, which is a non-human animal carrying a human hematopoietic prostaglandin D.sub.2 synthase gene in its somatic cell chromosome and expressing a large amount of human prostaglandin D.sub.2 synthase, wherein the animal is one obtained through ontogenesis of a totipotency cell of a non-human animal or offspring of the obtained animal, and the totipotency cell is introduced with said synthase gene. The present application also provides a method of using the transgenic animal for testing in vivo activity of a candidate for anti-allergy medicines, sleep-controlling substances and candidates for anti-obesity.