Connection structure for fluid device

Provided is a connection structure for a fluid device, the connection structure enabling a reduction in a space for mounting the fluid device. This connection structure for a fluid device is provided with: a cylindrical first receiving opening (11) provided to a first fluid device (1) so as to be in communication with a first fluid flow passage (21) of the first fluid device (1); a cylindrical second receiving opening (12) provided to a second fluid device (2) so as to be in communication with a second fluid flow passage (25) of the second fluid device (2); a first cylindrical member (13) having a first engagement section (53) and provided to the first receiving opening (11); a second cylindrical member (14) which has a second engagement section (54) capable of engaging with the first engagement section (53) and which is provided to the second receiving opening (12); and a connection body (15) which is provided between the first receiving opening (11) and the second receiving opening (12), seals against the f