Mitsubishi Heavy Industries, Ltd. (MHI), has developed a compact laser exhaust gas measurement device that can directly measure the gas temperature and concentration at high speed in engine pipes for furnace monitoring applications such as boilers and refuse incinerators. In this report, we describe the equipment and show, using case studies, how new insights have been provided by using it for exhaust gas measurement during transient operation of test bench engines or vehicles, in situations where data are difficult to obtain with conventional equipment. We also show the effectiveness of this equipment in the development of engine and exhaust gas treatment systems.