An event flow system connecting nodes, for which processes are defined, from an upstream side to a downstream side by an event which is generated due to a certain process and is used by another process to realize a process flow is provided. The event flow system includes: a process flow builder configured to build a process flow using a plurality of nodes, one or more events, and a reverse event that sends a predetermined request, from a downstream node to an upstream node disposed further toward an upstream side than the downstream node; and a process flow executer configured to execute a process defined for each of the plurality of nodes according to the event and the reverse event.