Preferably, said {TAIL ~ step} includes starting said {HEAD ~ speed changing operation} of said either one transmission mechanism when a down shift command for instructing a shifting to an at least two level lower shift position is output as the speed change command 
Preferably , said { TAIL ~ step } includes starting said { HEAD ~ speed changing operation } of said either one transmission mechanism when a down shift command for instructing a shifting to an at least two level lower shift position is output as the speed change command
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH