A drive unit for an automatic transmission has a hydraulic circuit changing device for changing a hydraulic circuit so that one of the hydraulic control portions (hydraulic gear change portions) is selectively communicated with an oil pressure source, a position detecting device for continuously detecting a position of one of moving members of the hydraulic circuit changing device and for outputting a detection signal corresponding to the position of the moving member, and a pressure regulating device provided between the hydraulic circuit changing device and the hydraulic control portions for regulating a control pressure to be applied to the hydraulic control portions. In the above drive unit, an electronic control unit calculates a rate of changes in the detection signals from the position detecting device and controls the pressure regulating device in accordance with the rate of the changes in the detection signals.