The on/off solenoid performs switching of the shift valve in the control valve body according to the vehicle conditions.
When the on/off solenoid is off, the supply port in the solenoid opens. As a result, hydraulic pressure is supplied to operate the shift valve.
When the on/off solenoid is on, the drain port in the solenoid opens. As a result, hydraulic pressure which operates the shift valve is drained.