1. An interframe prediction processor that performs interframe prediction of video frames on a block basis, comprising: a reference picture memory that provides vector storage locations corresponding to minimum size blocks to store reference motion vectors calculated for blocks of variable sizes; a reference picture storage manager that writes calculated motion vectors in the vector storage locations reserved in the reference picture memory; an address selector that provides memory addresses of the reference motion vectors in the reference picture memory 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, wherein: the predictor calculator requests the address selector to provide memory addresses of reference motion vectors calculated for specific adjacent blocks, the address selector comprises a translation table that associates each combination of block size and block location with a specific address of the reference picture memory, and the address selector determines the requested memory addresses of reference motion vectors stored in the reference picture memory, by looking up the translation table with information given by the predictor calculator.