A set of polycrystalline samples of Sr1-xLaxPbO3 (x<0.02) were prepared with special care taken in controlling the La content to within 0.2%. The measured resistivity () and thermopower (S) change systematically with x, and the x-dependences are explained consistently on the basis of a rigid-band picture in a single parabolic band. The carrier concentration evaluated ranges from 1019 to 1020 cm-3, while the scattering time and the mobility do not appreciably change with the La substitution. The power factor (S2/) takes a maximum at a carrier concentration of 4 × 1019 cm-3, which is nearly the same value as for conventional thermoelectric semiconductors. These data clearly indicate that carrier doping in SrPbO3 is as controllable as that in conventional semiconductors.