Ohmi, K. El Khechen, D. Hirosawa, K. Koiso, H. Ohnishi, Y. JACoW Publishing Geneva, Switzerland 978-3-95450-216-5 10.18429/JACoW-eeFACT2018-TUYBA01 English 103-105 TUYBA01 simulation MMI experiment luminosity synchrotron Contribution to a conference proceedings 2019 2019-04 https://doi.org/10.18429/JACoW-eeFACT2018-TUYBA01 http://jacow.org/eefact2018/papers/tuyba01.pdf Coherent beam-beam nstability in head-tail mode has been predicted in collision with a large crossing angle. The instability is serious for design of future e⁺e⁻ colliders based on the large crossing angle collision. It is possible to observe the instability in SuperKEKB commissioning. Horizontal beam size blow-up of both beams has been seen depending on the tune operating point. We report the measurement results of the instability in SuperKEKB phaseII commissioning.