Japan Aerospace Exploration Agency (JAXA) is currently developing the ALOS-2 follow-on L-band Synthetic Aperture Radar (SAR) mission, namely Advanced Land Observing Satellite-4 (ALOS-4). ALOS-4 aims to enhance the use of ALOS-2, such as improving disaster risk detection capability, by increasing swath width and temporal resolution with new technologies. JAXA is currently developing a flight model and is also considering ALOS-4 observation plan for the launch in JFY2021. In this presentation, we will report the outline of ALOS-4 L-band SAR observation, the observation plan, and the latest development status.