In situ experiments on the Co/SiC interface reaction were carried out with a high temperature X-ray diffractometer capable of measuring the X-ray diffraction pattern in 1-4s using an imaging plate. The kinetic formation processes of the interface reaction layer were measured in short-period exposure experiments with the apparatus. The time-temperature phase diagram of Co/SiC in N-2 was determined. Co2Si and CoSi were formed at the Co/SiC interface between 921 and 1573 K in N-2. The formation of CoSi obeyed the parabolic rate law. The value of the activation energy was 95 kJ/mol. The results of thermal expansion coefficient measurements suggest that when a sample is cooled to room temperature, compressive strain caused by CoSi occurs on SiC.