To surely prevent a fluid from leaking out of a flow passage of a flow passage structure.

The flow passage structure 1 is provided with: a first member 2 having a plate-like shape; a sheet member 3 to be laminated on the first member 2; and a plate-shaped pressing space member 4 being a second member to be laminated on the sheet member 3. The first member 2 and the pressing space member 4 are fixed to each other in such a state that they come into contact with the sheet member 3 in the flow passage structure 1. The sheet member 3 consists of a flexible sheet. The flow passage 11 is formed by covering a groove part 221 of the first member 2 with the sheet member 3. A pressing space 14 is formed to be superimposed on the groove part 221 by covering a concave part 41 of the pressing space member 4 with the sheet member 3. The pressing space 14 is packed with compressed air having the pressure higher than that of a reagent fluid flowing in the flow passage 11 and the sheet member 3 is pressed to the flow passage 11 by the packed compressed air. As a result, the reagent fluid can surely prevented from leaking out of the flow passage 11 between a flow passage member 22 of the first member 2 and the sheet member 3.