The present invention provides a charged particle beam apparatus capable of preventing the charging-up of the specimen without using a large-scale facility. A scanning electron microscope 100 illuminates a specimen 21 with a charged particle beam via a charged particle optical system arranged in a column. According to the present invention, the scanning electron microscope 100 has a charge preventive member 110 disposed between the objective lens 14 and the specimen 21. The charge preventive member 110 has an electrically conductive portion and an opening 113 to transmit the charged particle beam. The charge preventive member 110 is formed so as to partly cover the charged particle optical system when viewed from the charged particle beam irradiation spot on the specimen. In addition, the charge preventive member 110 has gas inflow paths 114 and 115 formed therein. These gas inflow paths have gas injection outlets 116 formed to inject gas toward the charged particle beam irradiation spot on the specimen.