We investigated the effects of a range of constant temperatures (13.3–32.5°C) on the development of all stages of Helicoverpa armigera (Kumamoto population) reared on tomato. The duration of the different life history stages decreased as temperature increased from 13.3°C to 32.5°C. A developmental threshold of 10.5°C, 11.3°C and 13.8°C was estimated for the eggs, larvae and pupal stages, respectively. A thermal constant of 51 degree-days above a threshold of 10.5°C was required for the development of the eggs. The larval stage required 215.1 degree-days and the pupal stage 151.8 degree-days above 11.3°C and 13.8°C developmental thresholds, respectively. Results from these studies may provide information important for predicting the field population phenology of H. armigera in Kumamoto Prefecture.