The Fortran compiler, version 10 has been replaced with the new one, version 12 (V12) on the Fujitsu Computer system at JAERI since May, 1992. The benchmark test for the performance of the V12 compiler is carried out with 16 representative nuclear codes in advance of the installation of the compiler. The performance of the compiler is achieved by the factor of 1.13 in average. The effect of the enhanced functions of the compiler and the compatibility to the nuclear codes are also examined. The assistant tool for vectorization TOP10EX is developed. In this report, the results of the evaluation of the V12 compiler and the usage of the tools for vectorization are presented. (author).