This paper deals with the control method for a newly designed module-type robot with a lazy tongs mechanism, the experimental results of passing over a reducer and the diagnostic results of the Mark V robot with the lazy tongs mechanism. This module-type robot has been newly designed for inspection of pipelines, such as pipelines for air conditioners and water pipelines, in buildings. This robot can recognize reducers by using a newly designed sensor to detect the reducers and can pass over the reducers automatically with no requirement for changing the parts of the robot. Passing the reducer and the change of a thickness of pipelines caused by corrosion are shown in the experimental results.