1. A motion prediction apparatus comprising: a similarity detector that detects block similarities indicating degree of similarities between a pixel block in a current frame and pixel blocks in a next frame; a smoothness detector that detects smoothness level of the pixel block in the current frame, the smoothness level indicating smallness of an image variance of the pixel block; a weighting unit that applies weights to each of the block similarities based on the smoothness level; and a motion vector determination unit that determines a motion vector of the pixel block in the current frame based on the weighted block similarities, wherein the weighting unit applies weights to the block similarities such that the motion vector determination unit tends to determine the motion vector having a small absolute value for the pixel block when the smoothness level of the pixel block is large.