Multiplication ratios (average number of harvestable propagules per stock plant) and electric energy consumption per harvestable propagule (single nodal cutting with an unfolded leaf, SNC) as affected by two propagation methods, propagation method using SNC only as propagules and propagation method using both SNC and stock plant base with an unfolded leaf (SPB) as propagules were investigated for sweetpotato (Ipomoea batatas (L.) Lam.) vegetative propagation in a closed transplant production system. Total number of harvestable propagules and electric energy consumption per harvestable propagule n multiplication cycles after the start of propagation (P (n) and E_p (n), respectively) were simulated for the two propagation methods, based on the results of the experiment : multiplication ratios were 1.8 and 3.7 for SNC and SPB, respectively, when a multiplication cycle was 12 d. P (10) were 89 to 197 times greater in the propagation method using both SNC and SPB than in the propagation method using SNC only. E (n) five or more multiplication cycles after the start of propagation in the propagation method using both SNC and SPB were reduced by 40% compared with those in the propagation method using SNC only. Results show that propagation method using both SNC and SPB as propagules in the system reduces the electricity cost and shortens the multiplication period.