Conventional charged particle beam devices are devices manufactured for dedicated use in performing observations in a gas environment that is at atmospheric pressure or a pressure virtually equal to atmospheric pressure, and there are no devices with which a typical high-vacuum charged particle microscope can be used to perform observations conveniently in a gas environment that is at atmospheric pressure or a pressure virtually equal to atmospheric pressure. Furthermore, with conventional methods it is not possible to perform an observation by means of a charged particle beam and an observation by means of light simultaneously with respect to the same location in a specimen placed in such an atmosphere. Therefore, the present invention is equipped with: a charged particle optical lens tube that illuminates a specimen with a primary charged particle beam; a vacuum pump that evacuates the interior of the charged particle optical lens tube; a removable membrane, which is arranged so as to separate the space where the specimen is arranged and the charged particle beam lens tube, and which is capable of transmitting or passing the primary charged particle beam; and an optical microscope, which is arranged on the opposite side of the charged particle optical lens tube with respect to the membrane and the specimen, and which has at least a portion of its light axis on the extension of the light axis of the charged particle optical lens tube.