This paper describes the development of a prototype of a test field for accessing the primary containment vessel (PCV) in the reactor building of Fukushima Daiichi Nuclear Power Stations (FDNPS). A possible access route to the inside of PCV includes CRD (Control Rod Drive) rail part for maintenance and exchange of CRD. In the practical tasks at reactor building Unit 2, remotely operated robots passed thorough there for the tasks. We designed test field that is a simplified CRD rail part with insertion section for the robot and constructed a prototype. In this paper, we described the design and the characteristics of developed prototype in detail.