A four-wheel drive apparatus for a vehicle with front wheels driven by an engine
comprises a generator connected to the engine for generating an electric current;
a motor driven by the electric current supplied from the generator and supplying
power for driving rear wheels; a battery charged by the electric current supplied
from the generator; a first relay switch for switching electric contact between
the generator and the motor; a second relay switch for switching electric contact
between the battery and the generator, wherein, the current generated by the generator
is alternatively supplied to the motor or the battery.