PURPOSE: To permit the soft start free from shock applied to a load by suppressing the switching of the revolution direction of the output shaft of a mechanical type continuously variable transmission which constitutes a motor- driven device until the output shaft revolves at a sufficiently low speed.

CONSTITUTION: A position detecting means LSz which outputs a detection signal when a speed change element (r) for speed-changing the revolution of the output shaft (o) of a mechanical type continuously variable transmission T shifts to the low speed side from a previously set position is provided, and a control circuit P for operating an electric conduction circuit for revolving an electric motor M in the normal or reverse direction only in the case where the detection signal is supplied from the position detecting means LSz is provided.