There is provided a sealing material for a thin plate member which eliminates the need to form seal grooves as in prior art when applied to a thin plate member such as a cell of a secondary battery such as a redox flow battery, a fuel cell and a lead storage battery, and which provides satisfactory sealing and can compactify and reduce in weight a device to be used and facilitate assembling with reduced cost as well as allowing more cells to be stacked resulting in improving fuel capacity. The annular sealing material for a thin plate member that provides sealing between thin plate members includes a lateral sealing body disposed on a lateral of the thin plate member, and a pair of sealing legs branching from the lateral sealing body in a fork shape and disposed on the front surface and the back surface of the thin plate member.