A transmission for a motor, the transmission receiving a rotational force from a rotational shaft of a motor to perform an output to an output shaft through shifting, and outputting the rotational force only in one direction at different shifting ratios according to forward/reverse rotation directions of the rotational shaft of the motor, the transmission comprising: a driving shaft having one or more one-way clutch contact surfaces formed on an outer periphery of a certain region of the driving shaft; a dual one-way clutch including a carrier for accommodating forward restrictors and reverse restrictors in both faces of the carrier, respectively, the forward and reverse restrictors, being radially equidistantly arranged with a predetermined phase angle difference, and a forward output ring and a reverse output ring disposed outside the forward restrictors and the reverse restrictors, respectively, to be selectively rotated according to a rotation direction of the driving shaft; and a low-speed rotational force transmitting means and a high-speed rotational force transmitting means including a plurality of gears,,, engaged with one another, the low-speed rotational force transmitting means and the high-speed rotational force transmitting means receiving the rotational force independently from the forward output ring and the reverse output ring of the dual one-way clutch so as to rotate the output shaft with the shifting ratios though different paths, whereby the dual one-way clutch allows a reverse input in a direction opposite to a rotation direction of an output of the output shaft characterized in that the carrier of the dual one-way clutch has a flange-shaped extension formed between the forward output ring and the reverse output ring, elastic bodies for elastically supporting balls toward the forward output ring and the reverse output ring are accommodated in the extension, and grooves, are formed on the forward output ring and the reverse output ring, respectively, wherein each of the grooves. corresponds to the ball and extends along an outer periphery of the corresponding output ring,. a driving shaft having one or more one-way clutch contact surfaces formed on an outer periphery of a certain region of the driving shaft; a dual one-way clutch including a carrier for accommodating forward restrictors and reverse restrictors in both faces of the carrier, respectively, the forward and reverse restrictors, being radially equidistantly arranged with a predetermined phase angle difference, and a forward output ring and a reverse output ring disposed outside the forward restrictors and the reverse restrictors, respectively, to be selectively rotated according to a rotation direction of the driving shaft; and a low-speed rotational force transmitting means and a high-speed rotational force transmitting means including a plurality of gears,,, engaged with one another, the low-speed rotational force transmitting means and the high-speed rotational force transmitting means receiving the rotational force independently from the forward output ring and the reverse output ring of the dual one-way clutch so as to rotate the output shaft with the shifting ratios though different paths, whereby the dual one-way clutch allows a reverse input in a direction opposite to a rotation direction of an output of the output shaft characterized in that the carrier of the dual one-way clutch has a flange-shaped extension formed between the forward output ring and the reverse output ring, elastic bodies for elastically supporting balls toward the forward output ring and the reverse output ring are accommodated in the extension, and grooves, are formed on the forward output ring and the reverse output ring, respectively, wherein each of the grooves. corresponds to the ball and extends along an outer periphery of the corresponding output ring,.