A method of obtaining a deflection aberration correcting voltage. The method includes writing predetermined patterns at a plurality of focus height positions such that a dose is used as a variable. Dimensional variations of width sizes of the predetermined patterns written at the plurality of focus height positions such that the dose is used as the variable are measured. Further, effective resolutions of the written predetermined patterns are calculated by using the dimensional variations. The method further includes, on the basis of a focus height position at which a minimum effective resolution of the predetermined patterns is obtained, calculating a correcting voltage to correct deflection aberration and outputting the correcting voltage. The correcting voltage is used when a charged particle beam is deflected.