The doubly-charged Higgs bosons [Formula: see text] are the typical particles predicted in the Georgi–Machacek (GM) model and their decay modes depend on the magnitude of the triplet vacuum expectation value (VEV) [Formula: see text]. In this paper, we focus on the study of their pair production process at the International Linear Collider (ILC): [Formula: see text], with the subsequent decay of two like-sign [Formula: see text] bosons through a pair of like-sign dileptons and the remaining two in their hadronic decays. The 5[Formula: see text] confidence level discovery reach at the ILC is also studied with two collision energies of 1.0 TeV and 1.5 TeV.