To provide an image processing apparatus capable of operating at high speed with lower cost as well as suppressing image quality degradation.

Original-image compression data input from an image input section 1 are converted to DCT data by a decoding/dequantizing section 2, and stored into an image memory section 3. A data selection part 11 in an image processing section 4 reads the DCT data stored in the image memory section 3, DCT data larger than a threshold value are selected and sent to a data arithmetic operation section 12, and the data arithmetic operation section 12 performs a given processing. With this, very small value and invalid coefficient data with a value 0 are not processed at the data arithmetic operation section 12, which can reduce the arithmetic operation. A block including data processed at the data arithmetic operation section 12 is compressed at an encoding/quantizing section 5, and sent to an image output section 6 for output.