Abstract. This study investigates economical introduction of nuclear fusion energy in the context of world energy supply and CO2 concentration. A long-term (during 21st century), 10 regional worldwide allocation energy/environment model Linealized Dynamic New Earth model is used for this study. Following nuclear fusion technological data are taken into consideration; cost of electricity (COE) and COE reduction rate, maximum regional plant capacity constraints, and regional introduction year. We simulated under atmospheric CO2 concentration 550 parts per million (ppm) targeted at year 2100 scenario. Result indicates that according to the cost bases for varieties of technologies from energy mining to energy generation of the LDNE model, the present-design tokamak-type reactors can be economically selected around 2050 to 2060 under 550-ppmv CO2 concentration constraint, and are not under all BAU (Business-As-Usual). It is revealed that breakeven prices of fusion reactors is increased by plus/minus some 10 to 30 mill/kWh under a 650-ppmv.