An experimental system for irradiating high-energy (4 MeV) helium beam was developed to investigate irradiation damage of tungsten by using tandem accelerator. In this system, particle fluence to a tungsten thin plate was achieved to 1022 ions/m2. Electron diffraction images were acquired for damaged tungsten using a transmission electron microscope (TEM) to measure the particle loading by helium irradiation. Crystal structure was qualitatively changed between helium irradiated area and non-irradiated area from diffraction patterns.