A method for processing a bitstream of a video signal by an apparatus, the method comprising: obtaining index information from the bitstream, the index information specifying a motion vector candidate to be used as a predicted motion vector of a current block; selecting at least one motion vector from at least one previously decoded spatial neighboring block; deriving a temporal motion vector from a temporal neighboring block; constructing a motion vector prediction candidate group of the current block, the motion vector prediction candidate group comprising a plurality of motion vector candidates including the selected at least one motion vector and the temporal motion vector; acquiring the predicted motion vector of the current block from the motion vector prediction candidate group, the predicted motion vector of the current block being the motion vector candidate specified by the index information; acquiring a motion vector of the current block based on the predicted motion vector; and decoding the current block based on the acquired motion vector, characterized in that selecting the at least one motion vector comprises: step (a): selecting the at least one motion vector based on at least one spatial neighboring block having a same reference picture list and a same reference picture as the current block; step (b): selecting the at least one motion vector based on at least one spatial neighboring block having a different reference picture list from the current block and the same reference picture as the current block when no motion vector is selected at step (a); step (c): selecting a scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the same reference picture list as the current block and a different reference picture from the current block when no motion vector is selected at step (a) and step (b); and step (d): selecting the scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the different reference picture list and the different reference picture from the current block when no motion vector is selected at step (a), step (b) and step (c). obtaining index information from the bitstream, the index information specifying a motion vector candidate to be used as a predicted motion vector of a current block; selecting at least one motion vector from at least one previously decoded spatial neighboring block; deriving a temporal motion vector from a temporal neighboring block; constructing a motion vector prediction candidate group of the current block, the motion vector prediction candidate group comprising a plurality of motion vector candidates including the selected at least one motion vector and the temporal motion vector; acquiring the predicted motion vector of the current block from the motion vector prediction candidate group, the predicted motion vector of the current block being the motion vector candidate specified by the index information; acquiring a motion vector of the current block based on the predicted motion vector; and decoding the current block based on the acquired motion vector, characterized in that selecting the at least one motion vector comprises: step (a): selecting the at least one motion vector based on at least one spatial neighboring block having a same reference picture list and a same reference picture as the current block; step (b): selecting the at least one motion vector based on at least one spatial neighboring block having a different reference picture list from the current block and the same reference picture as the current block when no motion vector is selected at step (a); step (c): selecting a scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the same reference picture list as the current block and a different reference picture from the current block when no motion vector is selected at step (a) and step (b); and step (d): selecting the scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the different reference picture list and the different reference picture from the current block when no motion vector is selected at step (a), step (b) and step (c). step (a): selecting the at least one motion vector based on at least one spatial neighboring block having a same reference picture list and a same reference picture as the current block; step (b): selecting the at least one motion vector based on at least one spatial neighboring block having a different reference picture list from the current block and the same reference picture as the current block when no motion vector is selected at step (a); step (c): selecting a scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the same reference picture list as the current block and a different reference picture from the current block when no motion vector is selected at step (a) and step (b); and step (d): selecting the scaled motion vector of the at least one spatial neighboring block based on at least one spatial neighboring block having the different reference picture list and the different reference picture from the current block when no motion vector is selected at step (a), step (b) and step (c).