A surface charge measuring distribution method includes the steps of irradiating a sample with a charged particle beam and charging a sample surface in a spot-like manner, irradiating the charged sample with the charged particle beam to measure a potential at a potential saddle point formed above the sample, selecting one of preset multiple structure models and a tentative space charge distribution associated with the selected structure model, calculating a space potential at the potential saddle point by electromagnetic field analysis using the selected structure model and tentative space charge distribution, comparing the calculated space potential and measured value to determine the tentative space charge distribution as a space charge distribution of the sample when an error between the space potential and the measured value is within a predetermined range, and calculating a surface charge distribution of the sample by electromagnetic field analysis based on the determined space charge distribution.