[en] Survey on usage of electronic journals was performed quantitatively by analyzing downloads accesses data to the 1,783 journals titles published by Elsevier in Japan Atomic Energy Agency (JAEA), 2006. Although JAEA researchers are interested in 1,028 journal titles among physics, chemistry, engineering, medicine, social sciences etc., it is found that 80% of total downloads was occupied by only 102 journal titles. To satisfy researcher's needs for electronic journals effectively, identification the core journals by librarians based on user's needs is rational way in cost. By shifting from print to electronic journals, the number of users increased by 30% and the number of papers read by researchers increased by 7 times. It is also found that many of researchers do not use SD (Science Directs) useful functions such as searching, linking to other bibliographic records, and alerting new information of electronic journals. To inform the useful functions to researchers by librarians is necessary. (author)