Recently, there has been a high demand for elucidating kinetics and visualizing reaction processes under extreme dynamic conditions, such as chemical reactions under meteorite impact conditions, structural changes under nonequilibrium conditions, and in situ observations of dynamic changes. To accelerate material science studies and Earth science fields under dynamic conditions, a submillisecond in situ X‐ray diffraction measurement system has been developed using a diamond anvil cell to observe reaction processes under rapidly changing pressure and temperature conditions replicating extreme dynamic conditions. The development and measurements were performed at the high‐pressure beamline BL10XU/SPring‐8 by synchronizing a high‐speed hybrid pixel array detector, laser heating and temperature measurement system, and gas‐pressure control system that enables remote and rapid pressure changes using the diamond anvil cell. The synchronized system enabled momentary heating and rapid cooling experiments up to 5000 K via laser heating as well as the visualization of structural changes in high‐pressure samples under extreme dynamic conditions during high‐speed pressure changes. A submillisecond X‐ray diffraction measurement system targeted at microscopic samples in a diamond anvil cell has been developed at BL10XU/SPring‐8. This system has enabled the visualization of structural changes of high‐pressure samples in the diamond anvil cell during instantaneous heating and quenching experiments combined with laser heating and during instantaneous compression and decompression experiments using a two‐line gas‐pressure control system, with a resolution in the submillisecond range.