There are provided a control device, a control method, a control unit, and an engine control unit, which are capable of controlling a controlled object with relatively large phase delay and dead time, while attaining elimination of lag in control timing between the input and output of the controlled object and improvement of control accuracy at the same time. A state predictor calculates a deviation (output deviation) between an output from an oxygen concentration sensor and a predetermined target value at a predetermined deviation calculation period. Then, a DSM controller calculates a target air-fuel ratio for converging the output from the oxygen concentration sensor to the predetermined target value, according to the calculated deviation, based on any one of a .DELTA. modulation algorithm, a .DELTA..SIGMA. modulation algorithm, and a .SIGMA..DELTA. modulation algorithm at a predetermined calculation period shorter than the predetermined deviation calculation period.