The I-V characteristics of　a diamond particle deposited by hot-filament chemical vapor deposition on a tungsten tip was measured in a dual-probe scanning electron microscope (DP-SEM) chamber by introducing Mo tips into the chamber as a measurement probe. The I-V characteristic of well crystallized diamond particle follows Ohm's law, and no field electron emission was observed, while the cauliflower-like particle satisfies the Pool-Frenkel (PF) theory and the field emission was observed clearly. These results are contributed to the defects in CVD diamond.