We have prepared a magnetic flux transformer that is operable at 77K by using commercially available RE123 High-T_c superconducting (HTS) tape. HTS seamless loop used in this study has been prepared by “Cut-and-wind” method, which enables to fabricate not only the large bore loop but also the multi-turn structure without jointing. The seamless loops constituting the transformer have diameter above 10 cm in this report. We have confirmed induction of superconducting shielding current in the loop for static field applying and magnetic field transferring by the flux transformer at 77K.