A sample observation method uses a charged particle beam apparatus comprising a charged particle optical column irradiating a charged particle beam, a vacuum chamber, and a sample chamber being capable of storing a sample. The method includes maintaining a pressure of the sample chamber higher than that of the vacuum chamber by a thin film which permits the charged particle beam to be transmitted, determining a relation between a height of a lower surface of the thin film and a height of a lower end of a lens barrel of an optical microscope, measuring a distance between the sample and the lens barrel, and setting a distance between the sample and thin film based on the relation and the distance.