A valve having a simple configuration that prevents the seat from being damaged by self-excited oscillation of the valve body and thus prevents seat leakage. The valve includes a valve casing having a fluid inlet, a fluid outlet, and a valve chamber; the valve chamber including a seat having a seat surface; a stem inserted into the valve casing so that the stem can be vertically movable; and a valve body arranged at a tip of the stem and capable of abutting on the seat surface of the seat due to the vertical movement of the stem such that a tip part of the valve body does not come into contact with the seat surface due to oscillation of the stem.