In a control apparatus for a powertrain that includes an automatic transmission, occurrence of slip in a one-way clutch is determined when one gear is formed if a first rotation member and a second rotation member of the one-way clutch rotate relatively. If slip in the one-way clutch is detected, it is determined whether the rotational speed difference between the first rotation member and the second rotation member has increased. If the rotational speed difference between the first rotation member and the second rotation member has increased when slip is detected in the one-way clutch, a control is executed to engage a predetermined frictional engagement element.