We investigate the galaxy overdensity around proto-cluster scale quasar pairs at high ( z > 3 ) and low ( z \sim 1 ) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program ( HSC-SSP ) . Using the first-year survey data covering effectively \sim 121 deg ^ { 2 } with the 5 \sigma depth of i \sim 26.4 and the SDSS DR12Q catalog , we find two luminous pairs at z \sim 3.3 and 3.6 which reside in > 5 \sigma overdense regions of g -dropout galaxies at i < 25 . The projected separations of the two pairs are R _ { \perp } = 1.75 and 1.04 proper Mpc , and their velocity offsets are \Delta V = 692 and 1448 km s ^ { -1 } , respectively . This result is in clear contrast to the average z \sim 4 quasar environments as discussed in \citet Uchiyama17 and implies that the quasar activities of the pair members are triggered via major mergers in proto-clusters , unlike the vast majority of isolated quasars in general fields that may turn on via non-merger events such as bar and disk instabilities . At z \sim 1 , we find 37 pairs with R _ { \perp } < 2 pMpc and \Delta V < 2300 km s ^ { -1 } in the current HSC-Wide coverage , including four from \citet Hennawi06 . The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high density ( > 4 \sigma ) regions . Thanks to the large sample size , we find a statistical evidence that this excess is unique to the pair environments when compared to single quasar and randomly selected galaxy environments at the same redshift range . Moreover , there are nine small-scale ( R _ { \perp } < 1 pMpc ) pairs , two of which are found to reside in cluster fields . Our results demonstrate that < 2 pMpc-scale quasar pairs at both redshift range tend to occur in massive haloes , although perhaps not the most massive ones , and that they are useful to search for rare density peaks .