A power-augmenting gear structure for an electric car includes a low-speed and power-augmenting transmitting route additionally installed in a gear case, with an output shaft of an electric motor extending in the gear case. The gear case has transmission gears forming conventional normal speed transmitting routes with normal speed reducing ratio for running on common flat roads, and a low-speed and power-augmenting transmitting route to be used in case of moving up an upward slope or coping with a condition needing a large torque. Then the electric motor may be reduced in its size, weight and cost, without necessity of enlarging it to have a large power.