The magma discharge step-diagram shows the relationship between time and cumulative eruption volume/mass of a volcano and is thought to be useful not only for evaluating volcanic activity but also for forecasting medium- to long-term future activity. However, the procedure and method for making the step-diagram has not been well described. Therefore, a unified procedure and method for making the step-diagram is proposed. First, the spatial distribution and activity period of eruption centers of a target volcano or volcano group should be defined. Then, the database that covers all the data of the eruption episode and/or eruptive stage of the volcano, such as age/duration of eruptive activity, mode of eruption, eruption volume and so on, is completed. Based on the database, several types of the step-diagrams can be created according to the purpose. Finally, it is recommended to publish both the diagram and the database as a set. As an example, we present the procedure to create the database and two types of step-diagrams of Usu volcano, long- and short-term ones. The short-term step-diagram shows the temporal change of the magma discharge rate during the historical activity since the 17th century, suggesting that the rate has been obviously decreased during the last 100 years of activity.
