In one embodiment, a method for measuring a resolution of a charged particle beam includes changing a focus position of the charged particle beam in a height direction, and scanning a dot mark formed on a substrate with the charged particle beam for each focus position, detecting a reflected charged particle reflected from the dot mark for each focus position, calculating a scattered charged particle distribution from a detection result of the reflected charged particle for each height corresponding to the focus position, performing a convolution operation on an approximate expression of a beam waveform of the charged particle beam and a mark shape of the dot mark, the approximate expression including an aperture angle and a resolution of the charged particle beam as parameters, and calculating the aperture angle and the resolution by fitting the scattered charged particle distribution by height and a calculation result of the convolution operation.