Satou, K. Mitsuhashi, T.M. JACoW Geneva, Switzerland Nondestructive beam profile monitoring is strongly requested for the proton machines, especially for the measurement of the high intensity high brightness beams. Ionization profile monitor is traditionally used for measurement of beam profile in the proton machines and proposed to measure the high intensity high brightness beams. The important issues are no uniformities of extraction field, velocity distribution of e⁻ from ionization process, the strong beam field and detection system, etc. In this talk, we will review recent developments on these issues from theoretical and experimental approach.