A check valve capable of improving the tightness between a sphere and a valve seat and suppressing the sinking is provided, so as to provide a liquid chromatography infusion pump enabling a high precision infusion even if in a low flow rate region. On a surface, contacted with the sphere, on the valve seat 10 of the check valve, a rim 10r is disposed around a through hole 10h in the center of the valve seat 10. The rim 10r is formed as a boundary between a concave spherical surface of a diameter Φ1 and a concave spherical surface of a diameter Φ2 disposed as concentric circles with the through hole 10h. When the sphere of a diameter ΦB abuts against the valve seat 10, the sphere 15 abuts against the valve seat 10 at the annular rim 10r in a line contact according to a relation of Φ1>ΦB>Φ2.