For correcting a defective portion in image data having a plurality of pixels, a plurality of first target pixels are selected one after another from normal pixels. Any defective pixel is detected within a predetermined area extending about each selected first target pixel as its center and also a normal pixel present on an extension line connecting the first target pixel and the defective pixel is detected and set as a second target pixel. For each defective pixel present between the first target pixel and the second target pixel, an interpolation value is calculated. Further, for each pair of the first target pixel and the second target pixel, a weight coefficient is calculated. The technique stores such plurality of interpolation values and weight coefficients. Then, by using the weight coefficient, a weighted average value of the interpolation values for each defective pixel is calculated and this weighted average value is used for the correction of each defective pixel.