1. A video decoding apparatus, comprising: a decoder configured to extract motion information on a current block to be decoded and a quantized frequency-transformed block from a bitstream; an inverse quantizer configured to reconstruct a frequency-transformed block based on inversely quantizing the quantized frequency-transformed block; an inverse transformer configured to reconstruct a residual block based on inversely transforming the frequency-transformed block; a predictor configured to determine a motion vector of the current block based on the extracted motion information, and generate a prediction block based on interpolating chroma sub-samples of a reference block referenced by the motion vector of the current block; and an adder configured to reconstruct the current block based on adding the reconstructed residual block and the prediction block, wherein the predictor is configured to calculate non-divided values of a first set of sub-samples by multiplying chroma integer-pixels by integer numerators and summing the multiplied chroma integer-pixels, derive the first set of sub-samples by dividing the non-divided values by a common denominator, and derive a second set of sub-samples by interpolation from the non-divided values of the first set of sub-samples, not from the first set of sub-samples which have been divided by the common denominator, and then division by the common denominator.