A data processing apparatus for treating a tread surface or a sidewall surface of a tire as a measurement surface, and processing data indicative of a shape of the measurement surface to evaluate a natural defect portion formed on the measurement surface, wherein the natural defect portion is an unintentional irregularity portion that is generated during a tire manufacturing process, the apparatus comprising: a sample point extraction unit for executing extraction processing on height data for one line obtained by scanning the measurement surface with a shape sensor every constant sampling period, the extraction processing comprising acquiring a continuous constant number of pieces of height data, started from a certain sample point as a start point, from the height data for one line, comparing each piece of the acquired height data with an average value of the acquired height data, and extracting a sample point having height data larger than the average value, wherein the sample point extraction unit is configured to execute the extraction processing in an entire region of the height data for one line while the start point is shifted, the apparatus being characterized by comprising: a natural defect candidate portion determination unit for executing determination processing of determining continuous sample points, included in the extracted sample points, as a natural defect candidate portion; and a differentiation unit for previously storing a condition characteristic of a shape of an intentional irregularity portion formed on the measurement surface, and executing differentiation processing comprising differentiating between the intentional irregularity portion and the natural defect portion using natural defect candidate portions, by excluding the natural defect candidate portion satisfying the condition from the natural defect candidate portions. a sample point extraction unit for executing extraction processing on height data for one line obtained by scanning the measurement surface with a shape sensor every constant sampling period, the extraction processing comprising acquiring a continuous constant number of pieces of height data, started from a certain sample point as a start point, from the height data for one line, comparing each piece of the acquired height data with an average value of the acquired height data, and extracting a sample point having height data larger than the average value, wherein the sample point extraction unit is configured to execute the extraction processing in an entire region of the height data for one line while the start point is shifted, the apparatus being characterized by comprising: a natural defect candidate portion determination unit for executing determination processing of determining continuous sample points, included in the extracted sample points, as a natural defect candidate portion; and a differentiation unit for previously storing a condition characteristic of a shape of an intentional irregularity portion formed on the measurement surface, and executing differentiation processing comprising differentiating between the intentional irregularity portion and the natural defect portion using natural defect candidate portions, by excluding the natural defect candidate portion satisfying the condition from the natural defect candidate portions. a natural defect candidate portion determination unit for executing determination processing of determining continuous sample points, included in the extracted sample points, as a natural defect candidate portion; and a differentiation unit for previously storing a condition characteristic of a shape of an intentional irregularity portion formed on the measurement surface, and executing differentiation processing comprising differentiating between the intentional irregularity portion and the natural defect portion using natural defect candidate portions, by excluding the natural defect candidate portion satisfying the condition from the natural defect candidate portions.