1. A video decoding apparatus, comprising: a prediction unit configured to: set a position of a first prediction block equal to a position of a coding block comprising a first prediction unit, and set a size of the first prediction block equal to a size of the coding block, in response to a size of a block indicated by parallel merge level information being greater than or equal to a first size and the size of the coding block being equal to a second size; derive, based on the position and the size of the first prediction block, a merging candidate relating to the first prediction block, the merging candidate comprising a spatial merging candidate; generate a merging candidate list for the first prediction block based on the merging candidate; and determine motion prediction information of the first prediction unit based on the merging candidate list.