Superconductivity in PrIr$_{2}$Zn$_{20}$ appears at $T_{rm c} = 0.05$ K in the presence of an antiferroquadrupolar order below $T_{rm Q} = 0.11$ K. We have studied pressure dependences of $T_{rm c}$, $T_{rm Q}$, and non-Fermi liquid behaviors in the resistivity $rho (T)$ by using two pressure transmitting media: argon maintaining highly hydrostatic pressure, and glycerol, which solidifies above 5 GPa producing nonhydrostatic pressure. Upon applying $P$ with argon up to 10.6 GPa, $T_{rm c}$ hardly changes, while $T_{rm Q}$ monotonically increases from 0.11 to 0.23 K. With glycerol, however, $T_{rm Q}$ and $T_{rm c}$ simultaneously fall below 0.04 K at 6.3 GPa. The contrasting results indicate that onsite quadrupolar fluctuations induce superconductivity in this compound.
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