The International Linear Collider (ILC) is the highest-priority next collider as a Higgs factory. In the linear collider, almost all accelerated particles that do not interact strongly at the collision point are not recycled and are all thrown into beam dumps, which is very different from the case of circular colliders. Therefore, a beam dump experiment in the linear collider can be performed in parallel with the main experiment, which has a great advantage in terms of statistics. In this study, we estimate the detection sensitivity to new light particles that interacts not only to primary electron beams but also to secondary photons, electrons, positrons, and muons in the ILC beam dump. This study demonstrates that the ILC beam dump experiment has an enhanced sensitivity to axion-like particles and leptophilic dark sectors by an order of magnitude compared with previous experiments and other future beam dump experiments.