A heat transfer tube life estimating system for estimating a life of a heat transfer tube of a boiler, the system comprising: an equivalent heat transfer coefficient calculating unit configured to calculate an equivalent heat transfer coefficient h e inside of the heat transfer tube based on a heat transfer tube temperature as a temperature of an outer wall surface of the heat transfer tube Tt 22; an equivalent heat transfer coefficient time change curve calibrating unit configured to calibrate an equivalent heat transfer coefficient time change curve representing a change in the equivalent heat transfer coefficient h e with time based on the equivalent heat transfer coefficient h e; a heat transfer tube temperature transition predicting unit configured to predict a transition in the heat transfer tube temperature based on the equivalent heat transfer coefficient time change curve which has been calibrated; and a creep life-time predicting unit configured to predict a creep life-time of the heat transfer tube based on a transition predicting data of the heat transfer tube temperature obtained by the heat transfer tube temperature transition predicting unit; wherein a heat conductivity of scale λ 2 [w/m • K] is constant, a temperature difference inside scale ΔT increases and the temperature of an outer wall surface of the heat transfer tube Tt 22 rises according to increase of a thickness of scale t 2 [m], a scale surface heat conductivity is h 2 [W/m 2 • K], and the equivalent heat transfer coefficient h e is represented by a formula h e = 1 / t 2 / λ 2 + 1 / h 2 W/m 2 ⋅ K, and wherein a fluid temperature is Tw, a heat flux q [W/m 2] is represented by a formula q= h e ΔT, wherein ΔT= Tt 22 -Tw. an equivalent heat transfer coefficient calculating unit configured to calculate an equivalent heat transfer coefficient h e inside of the heat transfer tube based on a heat transfer tube temperature as a temperature of an outer wall surface of the heat transfer tube Tt 22; an equivalent heat transfer coefficient time change curve calibrating unit configured to calibrate an equivalent heat transfer coefficient time change curve representing a change in the equivalent heat transfer coefficient h e with time based on the equivalent heat transfer coefficient h e; a heat transfer tube temperature transition predicting unit configured to predict a transition in the heat transfer tube temperature based on the equivalent heat transfer coefficient time change curve which has been calibrated; and a creep life-time predicting unit configured to predict a creep life-time of the heat transfer tube based on a transition predicting data of the heat transfer tube temperature obtained by the heat transfer tube temperature transition predicting unit; wherein a heat conductivity of scale λ 2 [w/m • K] is constant, a temperature difference inside scale ΔT increases and the temperature of an outer wall surface of the heat transfer tube Tt 22 rises according to increase of a thickness of scale t 2 [m], a scale surface heat conductivity is h 2 [W/m 2 • K], and the equivalent heat transfer coefficient h e is represented by a formula h e = 1 / t 2 / λ 2 + 1 / h 2 W/m 2 ⋅ K, and wherein a fluid temperature is Tw, a heat flux q [W/m 2] is represented by a formula q= h e ΔT, wherein ΔT= Tt 22 -Tw.