The instrumentation technology for process automation in the steel industry has been evolving with the demands of the times, adapting to its production process and its harsh environment as the latest measurement techniques applied by considering the physical measurement principles. Today, the instrumentation technology has become one of the essential technologies to maintain the competitiveness in the steel industry. In this review, the recent development trends and future prospects are described based on lectures and papers on process instrumentation technology published by the Iron and Steel Institute of Japan (ISIJ) in the last decade. The main challenges in recent steel processes were reducing greenhouse gas emissions, supplying high-quality products represented by high-strength steel sheets, and keeping stable operation without skilled workers. To meet these challenges, new measurement techniques that had been advanced in recent years, such as radio waves sensing, image processing, optical fiber sensors, and multivariate analysis, had been applied. The newly obtained process information contributes to further sophisticated processes automation, and is applied to Artificial Intelligence (AI) and Cyber-Physical Systems (CPS). In the next decade, it is hoped that the instrumentation technology will continue to make progress toward the establishment of a sustainable steel industry.