This article briefly introduces the International Linear Collider (ILC) cryomodules for superconducting RF cavities and the large-scale 2 K cryogenic system for the cryomodules. Fundamental ideas of continuous superfluid helium production are discussed using the example of the KEK-STF cryogenic system for superconducting RF cavity cryomodules, which provides a basic concept for large-scale superfluid helium cryogenic systems.