Abstract: A changeover valve can be switched to a state in which a second solenoid valve of normally-open type to normally control a second speed-change control valve for a high speed transmission train controls a first speed-change control valve for a low speed transmission train. An oil passage to switch the changeover valve to the state in which the first speed-change control valve is controlled by the second solenoid valve is connected to an oil passage on an output side of the second solenoid valve at a P or R position of a manual valve. When a system failure has occurred while a vehicle is running forward in that D, M position of the manual valve which is a forward running range, the high-speed transmission train is established by a high signal pressure of the second solenoid valve.