The potential effects of global warming on the occurrence of four types of Japanese pest insects were studied by developing a computer program. The number of generations of each insect under present thermal condition and after 2°C warming at 960 locations in Japan where temperature data was measured by the AMeDAS system was estimated. Thermal summation and daylength models were used to describe insect development and deleterious effects of low and high temperatures on the insects. In most regions, a non-diapausing insect, Plutella xylostella would complete two additional generations compared to the present. In a winter diapausing insect, Chilo suppressalis, the northern boundaries of zones of two and three generations would shift north-ward by about 300 km. A cold weather susceptible insect, Tribolium confusum, would expand its distribution area northward, but the northern front of its distribution would not shift markedly, except for in the central mountainous regions of the Main Island. Ephestia kuhniella, which is susceptible to hot weather, would not be able to occur in the western part of the Main Island and Shikoku and Kyushu Islands due to high temperatures in summer, leading to a large shrinkage in its distribution area in Japan. Our results demonstrated that the effects of global warming on insect occurrence would be significant, but should vary depending on the biological characters of the insects.