A method for measuring a lens aberration in a charged particle optical device including means that focuses an electron beam for two-dimensional scanning on a sample, the charged particle optical device comprising: an electron source for emitting an electron beam; sample mounting means for mounting the sample; electromagnetic lenses (3, 6, 7, 9a) including an aberration corrector and being disposed between the electron source and the sample mounting means; electron beam scanning means provided on an electron-optical upstream side of a lens (6, 9a) of the electromagnetic lenses (3, 6, 7, 9a) for which the aberration is to be measured, wherein said lens (6, 9a) includes the aberration corrector, said scanning means being adapted to scan and deflect the electron beam; beam diaphragm means (4; 24) provided upstream of the electron beam scanning means and adapted to focus the electron beam to a predetermined beam diameter; detecting means (8, 14, 15) adapted to detect an electron signal induced from the sample by the electron beam impinging onto the sample; and control means adapted to control the electron source, the electromagnetic lenses (3, 6, 7, 9a), the electron beam scanning means, and the detecting means (8, 14, 15), wherein the method for measuring a lens aberration comprises the following steps: scanning, by the electron beam scanning means, the electron beam from the electron source so as to two-dimensionally scan a beam probe on a surface of the sample, the beam probe being formed by the electromagnetic lenses (3, 6, 7, 9a), detecting, by the detecting means (8, 14, 15), at least one of signals including a secondary electron, a reflected electron, a transmitted electron, and a scattered electron that are induced by the beam probe projected with a distortion on the surface of the sample according to an aberration of the lens (6, 9a) for which aberration is to be measured, obtaining a two-dimensional scan image in synchronization with scanning on the lens (6, 9a) for which aberration is to be measured, said scan image being referred to as a scanning Ronchigram, and calculating, by the control means, an aberration amount of the lens (6, 9a) for which aberration is to be measured based on the scanning Ronchigram. an electron source for emitting an electron beam; sample mounting means for mounting the sample; electromagnetic lenses (3, 6, 7, 9a) including an aberration corrector and being disposed between the electron source and the sample mounting means; electron beam scanning means provided on an electron-optical upstream side of a lens (6, 9a) of the electromagnetic lenses (3, 6, 7, 9a) for which the aberration is to be measured, wherein said lens (6, 9a) includes the aberration corrector, said scanning means being adapted to scan and deflect the electron beam; beam diaphragm means (4; 24) provided upstream of the electron beam scanning means and adapted to focus the electron beam to a predetermined beam diameter; detecting means (8, 14, 15) adapted to detect an electron signal induced from the sample by the electron beam impinging onto the sample; and control means adapted to control the electron source, the electromagnetic lenses (3, 6, 7, 9a), the electron beam scanning means, and the detecting means (8, 14, 15), wherein the method for measuring a lens aberration comprises the following steps: scanning, by the electron beam scanning means, the electron beam from the electron source so as to two-dimensionally scan a beam probe on a surface of the sample, the beam probe being formed by the electromagnetic lenses (3, 6, 7, 9a), detecting, by the detecting means (8, 14, 15), at least one of signals including a secondary electron, a reflected electron, a transmitted electron, and a scattered electron that are induced by the beam probe projected with a distortion on the surface of the sample according to an aberration of the lens (6, 9a) for which aberration is to be measured, obtaining a two-dimensional scan image in synchronization with scanning on the lens (6, 9a) for which aberration is to be measured, said scan image being referred to as a scanning Ronchigram, and calculating, by the control means, an aberration amount of the lens (6, 9a) for which aberration is to be measured based on the scanning Ronchigram. scanning, by the electron beam scanning means, the electron beam from the electron source so as to two-dimensionally scan a beam probe on a surface of the sample, the beam probe being formed by the electromagnetic lenses (3, 6, 7, 9a), detecting, by the detecting means (8, 14, 15), at least one of signals including a secondary electron, a reflected electron, a transmitted electron, and a scattered electron that are induced by the beam probe projected with a distortion on the surface of the sample according to an aberration of the lens (6, 9a) for which aberration is to be measured, obtaining a two-dimensional scan image in synchronization with scanning on the lens (6, 9a) for which aberration is to be measured, said scan image being referred to as a scanning Ronchigram, and calculating, by the control means, an aberration amount of the lens (6, 9a) for which aberration is to be measured based on the scanning Ronchigram.