To efficiently separate an ash content in fly ash when unburned carbon in the fly ash is removed by applying a floatation method by surface reforming.

The unburned carbon removal method comprises a step for mechanically classifying/separating the unburned carbon b in the coal ash a using a classifier 1; a step for crushing or pulverizing the coal ash a a part of the unburned carbon removed by the classifier 1 by a crushing machine 10; a step for adding water c to the coal ash a crushed or pulverized by the crushing machine 10 to make a slurry; a step for adding a capturing agent e to the slurried coal ash a; a step for giving a shearing force to the slurry added with the capturing agent e to selectively deposit the capturing agent e onto the unburned carbon b in the coal ash a; a step for adding a bubbling agent f to the slurry after the capturing agent e is deposited on the unburned carbon b; and a step for stirring the slurry after addition of the bubbling agent and selectively floating/separating the unburned carbon b with the generated bubbles n.