[en] In the ROSA-IV program, preliminary operational tests of the Large Scale Test Facility(LSTF) were conducted starting in December of 1984. Small break loss-of-coolant accident simulation experiments were begun in April of 1985, and up to about 100 experiments are planned in the future. This report describes the data reduction and management software system(Version 1) developed for the LSTF experiments. This software system is currently implemented on the data acquisition and reduction system at the LSTF and on the mainframe computer at the JAERI computing center. After January of 1986, an optical data transfer link will be operational between the LSTF and the computing center, and up to about 400 MB(mega byte) of data per experiment will be processed on the mainframe computer. Accordingly, the data reduction and management software system(Version 1) will be updated to Version 2, which will be implemented in 1986. (author)