A cost model for a tokamak fusion power plant (FPP) is improved to evaluate material cost and manufacture cost, separately. Then, the improved cost model is applied to a commercial tokamak FPP, and reduction of FPP construction cost is investigated considering learning effect on manufacture of the fusion island part and the advanced manufacture of toroidal field (TF) coils. Finally, a development scenario of a tokamak FPP is proposed to contribute substantially to global climate stabilization under the framework of the Paris Agreement.