Precise measurement of HFS of positronium

Positronium is an ideal system for the research of the QED. The hyperfine splitting of positronium is sensitive to the higher order correction of the QED and to the new physics beyond the Standard Model via a vacuum oscillation. The new method of QED calculations has revealed the 3.5σ discrepancy between the QED prediction and the previous measurements. It might be because of the new physics or the experimental systematic uncertainties (the effect of unthermalized Ps and the nonuniformity of the magnetic fields). We present the results of the first run and the future plan of our new precise measurement on HFS without these uncertainties.