The effects of operating gas pressure on a Cylindrical Inertial Electrostatic Confinement Fusion (IECF) device are investigated. First we did glow discharge experiments, and we obtained 1.8 × 106 neutrons production per second with 45-kV, 44-mA discharge at 1.2 Pa. Next we modified the device and tried to reduce the operating gas pressure with an ion source, aimed to increase neutron production. Although the discharge currents are small, we can make steady discharges at less than 0.1 Pa. The neutron production rates per current are larger than those of glow discharge at higher pressure. We consider it should suggest the validity of reducing operating pressure in IECF devices.