[en] In Fukushima Daiichi Nuclear Power Station, before retrieval of molten fuel debris inside PCV, the operation such as decontamination, survey, repair and taking sample of fuel debris are implemented step by step. In case of investigation inside primary containment vessel (PCV), some remotely operated robots have been used for because human can't access to high radiation environment. Because a radiation dose is very high in PCV, therefore it is necessary to prevent the leak of radiation from PCV when a robot is inserted in PCV. Then a pipe of 100 mm inside diameter was let go through by the PCV wall, and the seal box which was completely sealed up attached to the end of pipe. The robot is put in the seal box beforehand and is inserted inside PCV through the pipe. So it is necessary for the robot to be small. In addition, it is necessary to be stable movement on rough plane inside PCV. Therefore shape change type robot 'PMORPH' was developed. This robot consists of three parts of the slim main body and two crawlers attached to the both ends of main body. When this robot is passed in the pipe, three parts lie in a straight line like 'I' shape. And when the robot moves on a rough plane, three parts are formed like 'U' shape. We minimized the use of electric parts in the main body against high radiation environment. And this robot carries a winch to let a sensor unit descend to basement floor. And we carried out the basement floor investigation (B2 investigation) using the robot to obtain information of fuel debris condition in March, 2017. As a result, some information of basement floor condition was acquired. In this paper, it is described the outline of the shape change robot and summary of the B2 investigation. (authors)