Transport properties of the manganites by the double-exchange mechanism are considered. The system is modeled by a simplified double-exchange model, i.e. the Hund coupling of the itinerant electron spins and local spins is simplified to the Ising-type one. The transport quantities such as the electronic resistivity, the thermal conductivity, and the thermal power are calculated by using the dynamical mean-field theory. The transport quantities obtained qualitatively reproduce the ones observed in the manganites. The results suggest that the simplified double exchange model underlies the key properties of the manganites.