  We use a graphics processing unit (GPU) for fast computations of Monte Carlo
integrations. Two widely used Monte Carlo integration programs, VEGAS and
BASES, are parallelized on GPU. By using $W^{+}$ plus multi-gluon production
processes at LHC, we test integrated cross sections and execution time for
programs in FORTRAN and C on CPU and those on GPU. Integrated results agree
with each other within statistical errors. Execution time of programs on GPU
run about 50 times faster than those in C, and more than 60 times faster than
the original FORTRAN programs.
