1. An interframe prediction processor that performs interframe prediction of video frames on a block basis, comprising: an address selector that provides memory addresses of reference motion vectors according to given coding type information about a current block pair and adjacent block pairs thereof, when performing motion vector prediction with reference to blocks outside the current block pair, and when given macroblock adaptive frame/field (MBAFF) identification type information indicates that a given picture is supposed to be processed in MBAFF mode allowing selection between frame prediction and field prediction for each individual block pair, wherein the coding type information indicates whether each block pair is organized in frame form or in field form; and a predictor calculator that determines a motion vector predictor for each constituent block of the current block pair based on reference motion vectors read out of the provided memory addresses.