QSOs are the most luminous objects in the Universe. The most luminous QSOs may reside in the most massive galaxies because the massive black holes statistically exist in the massive galaxies according to M-σ relation and their heavy masses accelerate the accretion. Nevertheless, this presumption has some uncertainty ; the reservoir of gas in the system of a galaxy is likely to be limited quantitatively, and there is also a possibility the gas supplied from the outside of the galaxy like cold stream or through the major merger flow into the accretion disk. That is, the activity of QSOs may depend on not only their own properties like the mass but also the ambient environment in/beyond the scale of a galaxy. However, it is nontrivial how large the ambient environment affect the mass accretion to the disk whose scale is much smaller than that of galaxy. Then we statistically try to characterize whether protoclusters host QSOs at high redshift or not. This study is based on wide-field imaging of Hyper Suprime-Cam(HSC). Thanks to this, we got enormous samples, 131 protocluster candidates at z~4. We firstly report about the correlation between QSOs and protocluster candidates at this epoch.