An automatic steel deck cutting system using a multi-axis robot for power plant construction work has been developed. This system uses a laser distance meter and a camera to recognize the shape of the steel deck and moves a plasma cutting torch attached on the tip of the robot to follow the unevenness of the deck. Many steel plates are embedded in the ceiling of the deck slab structure of power plants to fix equipment and piping. In order to expose these embedded steel plates during equipment installation work, it is necessary to cut the steel deck into square to match the outline of the steel plates. Conventionally, workers cut the steel deck using a gas cutting machine in an upward position, which was hard work and high risk of industrial accidents. Therefore, we decided to automate this work by combining a plasma cutting machine and a robot arm. However, steel decks are made of galvanized steel sheets several millimeters thick, and their dimensions vary from site to site. If the torch is not moved at the appropriate speed, position, and posture according to the shape of the deck, the plasma arc will break off and the cutting process will fail. Therefore, the system uses a laser distance meter and a camera to recognize the shape of the deck by image recognition. This paper describes the issues in automatic cutting of steel decks, the system configuration to solve the issues, the method of recognizing the deck shape by sensing, the results of parameter test to maintain the plasma arc during the cutting process, and the results of a steel deck cutting test using a prototype system combines these elements.