PURPOSE: To eliminate the need for a rotating speed arithmetic process and to enable secure and stable selecting operation by providing a pulse selecting circuit which selects one of pulses from two rotation sensors according to the pulse itself.

CONSTITUTION: The digital rotation detecting device consists of the pulse selecting circuit 20 which selects one of the pulses N1 and N2 from the two rotation sensors and a rotating speed detecting means. Then the gate control circuit 24 of the circuit 20, when receiving the pulse N1 from the 1st rotation sensor, outputs a control signal which inhibits the passage of the following pulse N2 from the 2nd rotation sensor to an output gate circuit 23, when the pulse N1 is not received but the pulse N2 is received successively, a signal which allows the passage of the pulse N2 is outputted to the circuit 23. Therefore, when the 1st rotation sensor is troubled and the pulse N1 is not outputted, the pulse N2 can be outputted as a backup signal, so the rotating speed detection can be continued. Further, the pulses are passed selectively under the control of the circuit 24 according to the pulses N1 and N2, so the rotating speed arithmetic process needs not to be interposed.