DLC films were deposited on cemented carbide substrate by Ionization Deposition from benzene source gas. Films were prepared at the condition that substrate bias voltage Vb was varied from 0 to -3000V. The film structure was examined by Raman spectroscopy and hardness was measured, and sliding test against Al-Mg alloy was performed. In case of Vb=0V, soft polymer carbon films were deposited, and in other bias voltage, DLC films, that was as hard as or harder than TiN film, were deposited. As a result of sliding test by ball-on-disk machine, it became clear that friction and wear property of DLC films against Al-Mg alloy were superior to that of no-coat cemented carbide substrate, or TiN film