A gate valve for vacuum and a seal member thereof, wherein the gate valve is capable of preventing the seal member from being cracked or particles from being produced due to stress concentration even if the seal member is repeatedly compressed in the state that the adhesive agent is separated from the open side of a seal member mounting groove and capable of suppressing particles from being produced due to the rub of the seal top part with the seal surface. In the gate valve for vacuum, the cross-section of the seal member is formed in a generally chevron shape with an apex (T). The gate valve is characterized in that an outer sloped surface (24d) is formed on the lateral outer side of the seal member mounting groove (23) corresponding to the apex (T), an inner sloped surface (24e) is formed on the lateral inner side of the seal member mounting groove (23) corresponding to the apex (T), the inclination of the outer sloped surface (24d) is theta1, the inclination of the inner side sloped surface (24e) is theta2, and the width of the bottom surface of the seal member mounting groove (23) is S, the apex (T) is positioned on the inner side of the seal member mounting groove (23) from the position by S/2, and theta1 is larger than theta2.