A method of verifying randomness of a bitstream is disclosed. The method includes receiving a bitstream consisting of n consecutive bits and dividing the bitstream into a plurality of bit blocks. In this case, n is a natural number of two or greater, each of the bit blocks consists of m consecutive bits, and m is a natural number of two or greater and is smaller than n. Further, the method includes allocating the plurality of bit blocks to a plurality of core groups in a graphics processing unit (GPU), processing the allocated bit blocks in the plurality of core groups in parallel, calculating random number level values of the allocated bit blocks, and determining whether the bitstream has randomness based on the calculated random number level values. Each of the core groups includes a plurality of cores capable of performing identical or similar tasks without separate synchronization.