A uniquely shaped gasket (6) suitable for a container for storage of substrate plates requiring precision packaging. When such plates are stored into a container body (2), and a container lid (3) is closed and then a lid lock is applied, a gasket's outward ledge (6b, 6c, 6d) is pressed downward by an outward adjacent surface (3f) and deformed; consequently, the end of the ledge's tip (6d) will extend to fall in a seal channel (2d), in other words, to abut on a sectionally downward concave (2d), wherein the gasket (6) still keeps its elastic resiliency. As a result, if an air pressure difference occurs, the tip end (6d) will shift its abutting point. While the tip end (6d) moves, a minimum gap between the tip end (6d) and the channel surface (2d) occurs, and this gap will act as ventilation route to equalize the air pressure difference.