To provide an image coder that can predict an optimum quantization parameter with high accuracy so as to reduce deterioration in image quality and effects of overflow/underflow even in a scene where a sudden change in a generated bit quantity is estimated such as at a scene change.

Before an image stored in a frame memory 11 is coded by a compression coding section 12, a tentative coding section 15 uses a tentative quantization parameter to encode the image. Then a bit quantity calculation section 16 calculates a bit quantity of a coded bit stream outputted from the tentative coding section 15, a quantization parameter prediction section 18 inputs an object bit quantity decided by a quantization control section 14 and a bit quantity calculated by the bit quantity calculation section 16 to predict an optimum quantization parameter by which the object bit quantity is coincident with the bit quantity outputted from the compression coding section 12 and to predict the optimum quantization parameter that is corrected, and the quantization control section 14 uses the quantization parameter to conduct quantization control.