procedure TForm1.ComboBox1DrawItem(Control: TWinControl;
 Index: Integer; Rect: TRect; State: TOwnerDrawState);
var
 strVal, strAll: string;
 pos1, pos2: Integer;
 rc: TRect;
 arrWidth: array [0..3] of Integer;
begin
 Combobox1.Canvas.Brush.Style := bsSolid;
 Combobox1.Canvas.FillRect(Rect);
 // the columns must be separated by ';'
 strAll := Combobox1.Items[Index];
 arrWidth[0] := 0;
 arrWidth[1] := 100; // Width of column 1
 arrWidth[2] := 200; // Width of column 2
 arrWidth[3] := 300; // Width of colimn 3
 // Drawingrange for first column
 rc.Left := Rect.Left + arrWidth[0] + 2;
 rc.Right := Rect.Left + arrWidth[1] - 2;
 rc. := Rect.;
 rc.Bottom := Rect.Bottom;
 // Get text for first column
 pos1 := Pos(';', strAll);
 strVal := Copy(strAll, 1, pos1 - 1);
 // Draw Text
 Combobox1.Canvas.TextRect(rc, rc.Left, rc., strVal);
 // Draw separating line betwenn columns
 Combobox1.Canvas.MoveTo(rc.Right, rc.);
 Combobox1.Canvas.LineTo(rc.Right, rc.Bottom);
 // Drawingrange for second column
 rc.Left := Rect.Left + arrWidth[1] + 2;
 rc.Right := Rect.Left + arrWidth[2] - 2;
 // Text fur zweite Spalte ausfiltern
 // Get text for second column
 strAll := Copy(strAll, pos1 + 1, Length(strAll) - pos1);
 pos1 := Pos(';', strAll);
 strVal := Copy(strAll, 1, pos1 - 1);
 // Text ausgeben
 // Draw Text
 Combobox1.Canvas.TextRect(rc, rc.Left, rc., strVal);
 // Trennlinie zwischen Spalten zeichnen
 // Draw separating line betwenn columns
 Combobox1.Canvas.MoveTo(rc.Right, rc.);
 Combobox1.Canvas.LineTo(rc.Right, rc.Bottom);
 // Drawingrange for third column
 rc.Left := Rect.Left + arrWidth[2] + 2;
 rc.Right := Rect.Left + arrWidth[3] - 2;
 // Get text for third column
 strAll := Copy(strAll, pos1 + 1, Length(strAll) - pos1);
 pos1 := Pos(';', strAll);
 strVal := Copy(strAll, 1, pos1 - 1);
 // Draw Text
 Combobox1.Canvas.TextRect(rc, rc.Left, rc., strVal);
 // Draw separating line betwenn columns
 Combobox1.Canvas.MoveTo(rc.Right, rc.);
 Combobox1.Canvas.LineTo(rc.Right, rc.Bottom);
 strAll := Copy(strAll, pos1 + 1, Length(strAll) - pos1);
end;

// Example/ Beispiel:
procedure TForm1.Button1Click(Sender: TObject);
begin
 with Combobox1.Items do
 begin
  Add('first;second;third;');
  Add('column1;column2;column3;');
 end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 //Oder im Objekt Inspektor einstellen
 //Or set this Property in the Object Inspector
 Combobox1.Style := csOwnerDrawFixed;
end;