A program for the fragment molecular orbital (FMO) calculation was developed that uses fine-grained parallelization to determine the electronic structure of large molecular systems such as proteins in practicable time. Using this program on a HITACHI SR8000 supercomputer, we found that the method improved the most time-consuming step, which is the calculation of molecular integrals, by a factor of 7. The improvement in the ERI eveluation was proportional to the number of processor units used in the calculations. Despite this improvement, clock time was not dramatically shortened because communication time in an HITACHI SR8000 is relatively slow.