The present invention enables a reduction in circuit scale.In an image coding apparatus (100), as for DCT coefficients as simple coded data obtained by coding an input image (91) by simple processing, the input image (91) is coded by at least quantizing the input image (91) as an input image on the basis of selected quantization parameters (QPl) discretely selected from quantization parameters (QP) as quantization factors, thereby computing generated code sizes of the input image (91) upon coding. The image coding apparatus (100) corrects an error in the generated code sizes of the input image upon coding which occurs in accordance with the simple processing, thereby computing low-precision generated code sizes. The image coding apparatus (100) computes low-precision generated code sizes when the input image (91) is coded on the basis of quantization parameters (QP) other than the selected quantization parameters (QPl), by an interpolation process with respect to the low-precision generated code sizes when the input image (91) is coded on the basis of the selected quantization parameters (QPl).