1. A coding method comprising: an input image complexity calculating step which calculates a complexity of an image of a first region of an input image; a coding unit complexity calculating step which calculates a complexity of an image of a coding unit in the first region of the input image; a quantization parameter calculating step of calculating a quantization parameter of the coding unit in the first region of the input image; and an encoding step of encoding the input image by using the quantization parameter calculated in the quantization parameter calculating step, wherein a size of the first region is changed based on a set target delay time, and wherein the quantization parameter calculating step calculates the quantization parameter based on the complexity of the image of the first region calculated in the input image complexity calculating step, the complexity of the image of the coding unit calculated in the coding unit complexity calculating step, an average quantization parameter value of a region of the input image prior to the first region and a code amount generated for the region of the input image prior to the first region.