1. An image processing apparatus comprising: an adjacent region setting unit that sets spatially adjacent regions on the basis of positions of prediction regions in a coding region so that generation of spatial motion vectors of the plurality of prediction regions is performed in parallel when a spatial prediction motion vector is generated among prediction motion vectors used to decode motion vectors of the plurality of prediction regions forming the coding region of an image; a prediction motion vector generation unit that generates a spatial prediction vector of the prediction region by using the motion vector of the spatially adjacent region set by the adjacent region setting unit; and a motion vector decoding unit that decodes a motion vector of the prediction region by using the prediction motion vector of the prediction region, wherein, in a case where a first prediction region is located on a right or lower side in the coding region, the adjacent region setting unit sets a first adjacent region of a second prediction region instead of the first adjacent region serving as the second prediction region located on a left or upper side in the coding region among adjacent regions of the first prediction region, and wherein the adjacent region setting unit, the prediction motion vector generation unit, and the motion vector decoding unit are each implemented via at least one processor.