A valve, comprising: a valve casing having a fluid inlet (Pi), a fluid outlet (Po), and a valve chamber; a seat provided in said valve chamber and having a seat surface; a stem (St) inserted into said valve casing so that the stem (St) can be vertically movable; and a valve body arranged at a tip of said stem (St) and capable of abutting on said seat surface of said seat due to the vertical movement of said stem (St); wherein the diameter of said valve body is greater than the diameter of said stem (St), wherein said valve chamber comprises a seat insertion part in which said seat is placed and a cylindrical part with a radius (Rcy) located above the seat insertion part, wherein said valve body comprises a truncated cone part opposed to said seat and an outer peripheral part having a larger diameter than that of the truncated cone part for fixing between said stem (St) and the truncated cone part, wherein the radius of the bottom surface of said truncated cone part is larger than the maximum radius (Rtmax) of said seat surface of said seat, wherein the radius (D/2) of the tip part of said truncated cone part is smaller than the radius (Rp) of the flow path of said seat, wherein the radius of said outer peripheral part is less than the radius Rcy of said cylindrical part and there is a gap for the flow of fluid from said fluid inlet to said fluid outlet between the outer peripheral part and the cylindrical part formed by the difference between the two radii, wherein the difference between the radius ( /2) of the tip part of the truncated cone part and the radius (Rp) of the channel of said seat is larger than the difference of the radius of the outer peripheral part and the radius (Rcy) of the above-mentioned cylindrical part so that the tip part of said valve body does not come into contact with said seat surface due to lateral oscillation of said stem (St). a valve casing having a fluid inlet (Pi), a fluid outlet (Po), and a valve chamber; a seat provided in said valve chamber and having a seat surface; a stem (St) inserted into said valve casing so that the stem (St) can be vertically movable; and a valve body arranged at a tip of said stem (St) and capable of abutting on said seat surface of said seat due to the vertical movement of said stem (St); wherein the diameter of said valve body is greater than the diameter of said stem (St), wherein said valve chamber comprises a seat insertion part in which said seat is placed and a cylindrical part with a radius (Rcy) located above the seat insertion part, wherein said valve body comprises a truncated cone part opposed to said seat and an outer peripheral part having a larger diameter than that of the truncated cone part for fixing between said stem (St) and the truncated cone part, wherein the radius of the bottom surface of said truncated cone part is larger than the maximum radius (Rtmax) of said seat surface of said seat, wherein the radius (D/2) of the tip part of said truncated cone part is smaller than the radius (Rp) of the flow path of said seat, wherein the radius of said outer peripheral part is less than the radius Rcy of said cylindrical part and there is a gap for the flow of fluid from said fluid inlet to said fluid outlet between the outer peripheral part and the cylindrical part formed by the difference between the two radii, wherein the difference between the radius ( /2) of the tip part of the truncated cone part and the radius (Rp) of the channel of said seat is larger than the difference of the radius of the outer peripheral part and the radius (Rcy) of the above-mentioned cylindrical part so that the tip part of said valve body does not come into contact with said seat surface due to lateral oscillation of said stem (St).