1. A caching method of graphic processing unit (GPU) having multiple cores wherein at least a part of pixels out of A*B pixels of video data are cached into a cache memory in order to perform image processing on k pixels of N*N size (where, k, N, A and B are natural numbers; k=N*N; A>N; B>N), the method comprising: grouping the at least a part of pixels out of A*B pixels into k pixel groups; mapping the k pixel groups to k cores of the GPU one-to-one basis by utilizing index information of each of the k pixels; and storing video data of the k pixel groups in the cache memory with reference to the mapping result, wherein the at least a part of pixels out of A*B pixels are grouped into the k pixel groups without any duplication, wherein the k pixel groups includes a plurality of horizontal pixel groups and a plurality of vertical pixel groups, and wherein each of the k cores chooses either the horizontal pixel groups or the vertical pixel groups by a first calculation using the index information of a pixel on which the image processing is to be performed.