PURPOSE: To reduce the transmission shock, by controlling the connecting condition of friction connecting elements for engine brake responding to the shift down condition whether it is in the acceleration or in the deceleration, in a shift down operation in a constant speed running.

CONSTITUTION: The feeding and exhausting of the operation oil to hydraulic actuators 41a to 46a to operate friction connecting elements are carried out by an oil pressure circuit 60. The oil pressure circuit 60 furnishes a manual valve 64 and shift valves 71 to 73, while the first to the third control lines 106 to 108 branched from a main line 100 furnish the first to the third solenoid valves 76 to 78 respectively, and these valves are turned ON or OFF responding to a shift stage to set, by signals A, B, and C from a control circuit 200 respectively. Therefore, when the shift down signal G is output from a constant speed running device 203, the signal G is decided whether it is for an acceleration or for a deceleration, and the solenoid valves 76 to 78 are operated.