This paper describes automatic coarse grain parallel process-ing on a shared memory multiprocessor system using a newly developed OpenMP backend of OSCAR multigrain parallelizing compiler for from single chip multiprocessor to a high performance multiprocessor and a heterogeneous supercomputer cluster. OSCAR multigrain parallelizing compiler exploits coarse grain task parallelism and near fine grain paral-lelism in addition to traditional loop parallelism. The OpenMP backend generates parallelized Fortran code with OpenMP directives based on an-alyzed multigrain parallelism by middle path of OSCAR compiler from an ordinary Fortran source program. The performance of multigrain par-allel processing function by OpenMP backend is evaluated on an off the shelf eight processor SMP machine, IBM RS6000. The evaluation shows that the multigrain parallel processing gives us more than 2 times speed up compared with a commercial loop parallelizing compiler, IBM XL Fortran compiler, on the SMP machine.