The purpose of the present invention is to provide a charged particle beam device and a sample holder for the charged particle beam device by which it is possible to form various environments, and perform in-situ observation and analysis without removing a sample from the charged particle beam device. In the present invention, inserting a detachable reverse side entry portion from a side facing a sample holding means, said portion being provided with a function for changing the state of a sample attached to the sample holding means, makes it possible to observe/analyze changes in the sample by a different process without removing the sample from the charged particle beam device by combining a reverse side entry portion having a different function with the sample holding means. The reverse side entry portion comprises two parts, and a tip thereof, which is one of the parts, is removable. After mounting the reverse side entry portion onto the sample holding means, the sample can be transported while maintaining the same atmosphere, and the sample can be transported between different devices without exposing the sample to air.