1. An image coding method of coding a target image including a luminance component and color difference components, the method comprising: acquiring a reference image; and generating a predicted image by interpolating the luminance component and the color difference components in the reference image according to a motion vector, wherein if a size of a block, which is designated as a unit of the interpolation, is equal to or smaller than a predetermined first threshold value, the generating includes inhibiting a bi-directional prediction, and performing only a uni-directional prediction, to generate the predicted image according to the motion vector.