1. A device configured to encode video data, the device comprising: a generator configured to generate a prediction block of a current prediction unit using a reference index and a motion vector of the current prediction unit, and a residual block using a difference between the current prediction unit and the prediction block; a transformer configured to transform the residual block to generate a transform block; a quantizer configured to quantize coefficients of the transform block to generate a quantization block using a quantization parameter, wherein the quantizer generates the quantization block by selecting two effective quantization parameters that are available and exist among left, upper, and previous quantization parameters according to an order of priority levels set for the left, upper, and previous quantization parameter and using an average of the two effective quantization parameters; and an entropy-coder configured to entropy-code the quantization block using a scan pattern, wherein the motion vector is encoded using a motion vector predictor which is set equal to one of an effective spatial motion vector candidate and an effective temporal motion vector candidate.