In order to observe a water-containing sample with excellent convenience under an air atmosphere or a gas atmosphere, or under a desired pressure, in the present invention, there is provided an observation support unit for observation by irradiating the sample disposed in a non-vacuum space separated by a diaphragm from an inner space of a charged particle optical lens barrel that generates a charged particle beam, with the charged particle beam. The observation support unit includes a main body portion for covering a hole portion that forms an observation region where the sample is observed, and the sample, and the observation support unit is directly mounted between the sample and the diaphragm, that is, on the sample.