Abstract: An ion beam analyzing apparatus wherein a scan image displayed on display means and the profile of an ion beam can be made coincide with each other readily to assure a high operability. Slit members for X and Y directions of an objector collimator are provided for movement to vary the dimensions of slits defined thereby, and dimensions A and B of the slits in the X and Y directions are detected. Dimensions X' and Y' of a spot of an ion beam irradiated upon a specimen on a target are calculated by multiplying the dimensions A and B by reduction ratios fx and fy of quadruple pole magnetic lenses, respectively, and then the dimensions X' and Y' are multiplied by values obtained by division of conditions Cx and Cy of an image apparatus by current scanning widths Sx and Sy of deflecting electrodes to calculate enlarged beam spot diameters X" and Y" respectively. An image having the diameters X" and Y" is displayed on a cathode ray tube so that an operator can visually grasp it.