To improve the sealability by providing a bead comprising a rubber- like elastic member to be attached/detached to/from a valve seat on a seal part of a valve element, and integrating a seal lip higher than the bead with a transfer fluid side of the bead to prevent the leakage of a transfer fluid in closing a valve while permitting the defective forming.

A seal member 21 comprising a rubber-like elastic member is fitted to a lower surface of a seal part 8a of a valve element 8, a bead to be attached/detached to/from a valve seat 22 is integrated with the seal member 21, and a seal lip 24 higher than the bead 23 is integrated with a transfer fluid side, i.e., an inner circumferential side of the bead 23. Even when any forming inconveniences such as inclination and distortion are present in the valve seat 22, and the bead 23 can not be brought into contact with the valve seat 22 in closing a valve, the seal lip 24 follows the inclination or distortion of the valve seat 23, and is brought into contact with the valve seat 22. Excellent sealability over the whole circumference of the valve seat 22 can be ensured, and the transfer fluid can surely be prevented from leaking between the valve seat 22 and the valve element 8 in closing the valve.