The lattice damage of a diamond crystal, caused by the analysis beam of helium ions with 2.0 MeV, 3 nA at room temperature, was characterized by nondestructive optical absorption topographic imaging that used position-sensitive scanning spectroscopy in the transmission mode. The result showed that the atomic structure and electronic states in diamond have been significantly changed by the ion beam, even at very low dose or dose rate. The measurement has been applied to the artificial diamond crystal.(type Ib) to evaluate how the damage induced by Rutherford backscattering/channeling, and the comparison to ion implantation (H-2(+)) is given. We found that a high column image, which reflects the defective states in irradiated synthetic diamond, provides a qualitative estimation of damage.