PURPOSE: To secure safety when a shift position detector is abnormal, by setting the shift position in the reverse position in starting of an engine when all bits of an output signal from the shift position detector is in their off state, and setting the shift position to the shift position evacuated to a memory means during the operation of the engine.

CONSTITUTION: In a control circuit 20 of a continuously variable transmission, an R range is set in the memory range for evacuation of the shift position variable, into which an output signal from a shift position detector 16 is to be stored in starting of an engine. Next, the output signal is read from the shift position detector 16 into the shift position variable, so as to take out the subordinate six bits of the shift position variable. Whether or not all six bits wherein the shift position variable corresponds to the shift position is in the off state is judged. When the result is YES, the shift position held in the evacuation range is set by the shift position variable. Moreover, when the engine is operated, for example, when the just before shift position is in the D range, the D range is set by the shift position variable.