Host galaxies of high redshift quasars (QSOs) are of interest. These very luminous black holes provide us with a valuable opportunity to investigate the physics relevant to the starburst-active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here we report an optical detection of an extended structure around a stacked QSO image. We have stacked 46 high-z (zmedian = 6.13) QSOs images by Subaru/Hyper Suprime-Cam. These QSOs are mainly identified by the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z-band extends for more than 4" on the sky (Re = 9.3kpc). The stacked host may be a forming giant galaxy, co-evolving with a supermassive black hole. More analysis will be carried out in the future.