An image processing apparatus which reduces an operation amount while maintaining accuracy in detecting a motion vector, includes a contrast value calculating circuit calculating a contrast value for each processing region including a pixel of interest at a center in a standard image which is one of input images, a bit length determining circuit determining a bit length for calculating a motion vector for the pixel of interest among the images to be smaller than a bit length when the contrast value is calculated, a quantization circuit converting a bit length of the processing region and a region corresponding to at least the processing region among the images to be the bit length determined by the bit length determining circuit, and a motion vector calculating circuit calculating a motion vector for the pixel of interest among the images in the processing region for which the bit length is converted.