Abstract: There is disclosed a one-hand openable and closable umbrella which does not cause relative rotational movement and displacement between an inner shaft and an outer shaft. The inner shaft has a U-shaped groove extending in the lengthwise direction thereof and the outer shaft has a convex block provided inside a lower nest mounted on the top of the outer shaft. By the engagement of the convex block of the outer shaft with the U-shaped groove of the inner shaft, the inner and outer shaft neither turn nor displace relative to each other when the latter slides on the latter. Moreover, since a plastic sleeve is put on the upper end portion of the inner shaft inside a spring mounted thereon, any frictional force between the spring and the inner shaft and between the spring and an upper nest can be decreased, by which the umbrella can be smoothly opened and closed.