A charged particle beam apparatus comprising a preparatory evacuation chamber (15 in FIG. 1A) into which a sample (12) is conveyed and which is preliminarily evacuated, an ultraviolet irradiation unit (21) which is disposed in the preparatory evacuation chamber (15) and which irradiates the surface of the sample (12) conveyed into the preparatory evacuation chamber (15), with ultraviolet rays for a predetermined time period, and a sample chamber (16) into which the sample (12) is conveyed in the preliminarily evacuated state of the preparatory evacuation chamber (15) or from which the sample (12) is conveyed into the preparatory evacuation chamber (15), wherein the ultraviolet irradiation of the sample (12) by the ultraviolet irradiation unit (21) is performed before the conveyance of the sample (12) into the sample chamber (16), or/and after the conveyance thereof from the sample chamber (16), thereby to remove contamination on the surface of the sample (12).