We have re-investigated the electrical resistivity ρ and the magnetic susceptibility x of the spin-ladder cuprate Sr14-xAxCu24O41 (A=Ca, Y, La), consisting of two-dimensional Cu2O3 ladder planes and one-dimensional CuO2 chains. The dlnρ/d(1/T) vs. T plot exhibits a broad peak around 200 K for x = 0. The peak temperature Tρ goes down with increasing hole-concentration p in the ladder for x(Ca)> 0, while it goes up with decreasing p in the ladder for x(Y, La)> 0. The observed Tρ is regarded as a temperature below which holes in the ladder are localized. On the other hand, the x-1 vs. T plot exhibits inflection indicating deviation from the Curie-Weiss law around 200 K for x = 0. The inflection temperature Tx also goes down with increasing p in the ladder, and goes up with decreasing p in the ladder. The observed Tx is regarded as a temperature above which Cu2+ spins in the ladder notably contribute to the susceptibility. Values of Tx and its x-dependence have been found to be almost the same as those of Tρ. This coincidence strongly suggests that holes in the ladder are paired and localized at low temperatures below Tx (and Tρ) where almost all Cu2+ spins in the ladder complete to form spin-singlet pairs.