A search for long-lived particles at the electroweak scale, which are predicted by a number of theories beyond the Standard Model,such as long-lived gluino in Split Supersymmetry, is presented. The search uses 32.7 $\rm{fb}^{-1}$ of 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC, and explores a multi-track vertex displaced from the collision point of proton-proton beams. The observed yield is consistent with the expectation from the background only hypothesis, resulting in 95\% confidence-level exclusion of the long-lived gluino with masses up to 2.4 TeV at around $\tau=0.17$ ns.