A fluid-device connecting structure includes a first fluid device having a first connection part, a second fluid device having a second connection part, an annular seal member to connect the first and second connection parts, and a coupling member to keep the first and second connection parts in a connected state. The coupling member includes a first coupling segment and a second coupling segment, each including at one end a first hinge part or a second hinge part. The first and second connection parts each have a cylindrical outer shape. The first coupling segment has a U-like shape having an opening and surrounds the first and second connection parts over a range more than 180 degrees of an entire circumference of each of the first and second connection parts.