Disclosed is a flow-type energy storage device having an improved flow of fluid. The flow-type energy storage device stores electricity using a fluidic material, and includes a reaction region in which charge-discharge reaction of electricity is performed by the fluidic material, wherein the reaction region has an octagonal cross-section. The shape of the reaction region is controlled to thus improve the flowability of the fluidic material, thereby providing a flow-type energy storage device that has almost constant electrical properties even when a charging and discharging cycle is repeatedly performed. Further, the structures of an inlet and an outlet are not complicated and a separate part for controlling the flow of fluid is not used in the device, and accordingly, additional costs are not incurred during a process of manufacturing the flow-type energy storage device.