description for brevity of explanation description will be made of the way of detecting the point of starting the shift operation and the point of ending up the shift operation the point of starting the shift operation is detected by continuously determining the theoretically virtual number of revolutions of the turbine n t 3 as indicated by the broken line c in fig5 on the basis of calculation at the third speed stage prior to the shift and comparing the virtual number of revolutions of the turbine n t 3 with an actual number of revolutions of the turbine n t as indicated by the broken line d in fig5 as the difference between the virtual number of revolutions of the turbine n t 3 and the actual number of revolutions of the turbine n t is recognized as a result of comparison then it is determined that the shift operation has started in fig5 the point e is the point where the shift operation has been regarded as starting on the other hand the point of ending up the shift operation is detected by continuously determining the theoretically virtual number of revolutions of the turbine n t 4 as indicated by the broken line f in fig5 on the basis of calculation at the fourth speed stage subsequent to the shift and comparing the virtual number of revolutions of the turbine n t 4 with an actual number of revolutions of the turbine n t the shift operation is regarded as having been ended when the difference between the virtual number of revolutions of the turbine n t 4 and the actual number of revolutions of the turbine n t has been recognized as a result of comparison the.