A control device for an automatic transmission including a transmission mechanism, and a torque converter which is disposed between an internal combustion engine that is a driving source of a vehicle, and the transmission mechanism, and which includes a lockup clutch, the control device comprising: a control means configured to control the automatic transmission in accordance with a traveling state of the vehicle; a rotation sensing means (80,84,8h) configured to sense a rotation speed difference (ΔN) between input and output elements of the lockup clutch; and a torque sensing means (86;91) configured to sense an output torque of the internal combustion engine, the control means including: a first engagement control section configured to perform a first engagement control when the lockup clutch is returned to a full engagement state after the full engagement state of the lockup clutch is temporarily released by an ON operation of the accelerator at a deceleration of the vehicle and a rotation of the internal combustion engine is then increased while the lockup clutch is in a slip engagement state, wherein the first engagement control brings the lockup clutch to the full engagement state while a torque transmission capacity (C LU) of the lockup clutch is increased, and a torque judging section configured to judge whether or not the output torque of the internal combustion engine is increased, characterized in that the control means also includes: a second engagement control section configured to perform a second engagement control to modify the first engagement control by adding a predetermined capacity to the increased torque transmission capacity (C LU) when the torque judging section judges an increase of the output torque of the internal combustion engine in a state where a sensed rotation speed difference (ΔN) sensed by the rotation sensing means (80,84,8h) in the slip engagement state of the engagement state of the first engagement control is increased to be equal to or greater than a first predetermined value (ΔN1) after a start of the control, and then decreased to be equal to or smaller than a second predetermined value (ΔN2) smaller than the first predetermined value (ΔN1). a control means configured to control the automatic transmission in accordance with a traveling state of the vehicle; a rotation sensing means (80,84,8h) configured to sense a rotation speed difference (ΔN) between input and output elements of the lockup clutch; and a torque sensing means (86;91) configured to sense an output torque of the internal combustion engine, the control means including: a first engagement control section configured to perform a first engagement control when the lockup clutch is returned to a full engagement state after the full engagement state of the lockup clutch is temporarily released by an ON operation of the accelerator at a deceleration of the vehicle and a rotation of the internal combustion engine is then increased while the lockup clutch is in a slip engagement state, wherein the first engagement control brings the lockup clutch to the full engagement state while a torque transmission capacity (C LU) of the lockup clutch is increased, and a torque judging section configured to judge whether or not the output torque of the internal combustion engine is increased, a first engagement control section configured to perform a first engagement control when the lockup clutch is returned to a full engagement state after the full engagement state of the lockup clutch is temporarily released by an ON operation of the accelerator at a deceleration of the vehicle and a rotation of the internal combustion engine is then increased while the lockup clutch is in a slip engagement state, wherein the first engagement control brings the lockup clutch to the full engagement state while a torque transmission capacity (C LU) of the lockup clutch is increased, and a torque judging section configured to judge whether or not the output torque of the internal combustion engine is increased, characterized in that the control means also includes: a second engagement control section configured to perform a second engagement control to modify the first engagement control by adding a predetermined capacity to the increased torque transmission capacity (C LU) when the torque judging section judges an increase of the output torque of the internal combustion engine in a state where a sensed rotation speed difference (ΔN) sensed by the rotation sensing means (80,84,8h) in the slip engagement state of the engagement state of the first engagement control is increased to be equal to or greater than a first predetermined value (ΔN1) after a start of the control, and then decreased to be equal to or smaller than a second predetermined value (ΔN2) smaller than the first predetermined value (ΔN1).