Seal structure and backup member

A seal structure for partitioning a high-pressure side and a low-pressure side, the seal structure, as viewed in a vertical cross section, comprising:

• one member having a first seal surface;
• a seal groove formed in the first seal surface;
• a sealing member attached in the seal groove and disposed on the high-pressure side;
• a backup member attached in the seal groove and disposed on the low-pressure side;
• and
• the other member disposed opposite the one member and having a second seal surface abutting the sealing member, wherein
• the seal groove has:
• a high-pressure side groove bottom on the high-pressure side at a certain distance from the second seal surface;
• and
• a low-pressure side groove bottom continuing the high-pressure side groove bottom on the low-pressure side, wherein the low-pressure side groove bottom becomes closer to the second seal surface in a direction from the high-pressure side groove bottom toward the low-pressure side, wherein
• the sealing member is disposed between the high-pressure side groove bottom and the second seal surface,
• the backup member is disposed between the low-pressure side groove bottom and the second seal surface,
• the backup member has an abutment surface on a side opposite the low-pressure side groove bottom, the abutment surface having a shape along the low-pressure side groove bottom, and
• the low-pressure side groove bottom has an arc shape.