An input shaft rotating speed detector detects an input shaft rotating speed Nin of an automatic transmission based on output signals from a resolver within a predetermined time period dt1. An output shaft rotating speed detector calculates the number of pulse signals output from an electromagnetic pickup sensor within the predetermined time period dt1, to detect an output shaft rotating speed Nout of the automatic transmission based on the time length of pulse intervals in the calculated number of pulse signals. With this configuration, the number of pulse signals used for calculating the output shaft rotating speed Nout can be changed, to thereby make a detection period of the output signals from the resolver used for calculating the input shaft rotating speed Nin be consistent with that of the pulse signals used for calculating the output shaft rotating speed Nout.