A magnetron discharge as a built-in ion source have studied both experimentally and numerically for a compact discharge-type fusion neutron source called IECF (Inertial Electrostatic Confinement Fusion). With this magnetron discharge, ions are produced in the vicinity of the vacuum chamber (anode) at negative electric potential. Therefore, produced ions are expected to have nearly full energy corresponding to the applied voltage to the IECF cathode but slightly smaller energy preventing them from hitting the anode of the opposite end, eventually improving both fusion reaction rate and ion recirculation life. Also, the magnetron ion source was found to produce ample ion current for maintenance of the discharge. With the optimization of the configuration of the magnetron discharge, further improvement of the fusion reaction rate is found feasible.