To obtain the moving image coder in which image quality of a decoded image is improved at low rate coding and detection accuracy of a motion vector is maintained even when image quality of the decoded image is deteriorated to generate a predicted image with a small prediction error.

The coder is provided with a frame memory 1a storing plural input images, a 1st motion vector detector 10b using the plural images stored in the frame memory 1a to detect a motion of the images, and a 2nd motion vector detector 10c correcting a motion vector outputted from the 1st motion vector detector 10b, and generates a predicted image by using the 2nd motion vector. Furthermore, a DCT transformation coefficient is used to obtain an evaluation indicating a difference between the predicted image and the input image so as to discriminate a valid block.