A pair of triply charmed baryons, $Omega_{ccc}Omega_{ccc}$, is studied as an ideal dibaryon system by (2+1)-flavor lattice QCD with nearly physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The spatial baryon-baryon correlation is related to their scattering parameters on the basis of the HAL QCD method. The $Omega_{ccc}Omega_{ccc}$ in the ${^1S_0}$ channel taking into account the Coulomb repulsion with the charge form factor of $Omega_{ccc}$ leads to the scattering length $a^{rm C}_0simeq -19~text{fm}$ and the effective range $r^{rm C}_{mathrm{eff}}simeq 0.45~text{fm}$. The ratio $r^{rm C}_{mathrm{eff}}/a^{rm C}_0 simeq -0.024$, whose magnitude is considerably smaller than that of the dineutron ($-0.149$), indicates that $Omega_{ccc}Omega_{ccc}$ is located in the unitary regime.
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