To provide a coder and a coding method that can minimize a side effect by emphasis processing and enhance the image quality of a reproduced image after decoding.

The emphasis level is set by a quantization parameter in the coding of an incoming image. When quantization is rough, strengthening the emphasis can suppress occurrence of block distortion and mosquito noise. When the quantization is fine, weakening the degree of the emphasis can suppress increase in a generated code quantity so as to decrease occurrence of side effects due to the emphasis.