A combined-blade open flow path device is a fluid flow path device where flow paths are adjacent to each other. The combined-blade open flow path device comprises a substrate configured to constitute a bottom portion of the flow paths; and blades erected on a surface of the substrate, the blades being configured to constitute side walls of the flow paths, wherein the blades are erected in groups, each of the groups extending from an upstream side to a downstream side in a flow direction of a fluid with a space between each of the blades in the flow direction of the fluid in each of the groups for making conduction of the fluid between the adjacent flow paths possible, and wherein one end of one of the flow paths is configured to be in contact with the fluid and is configured to make a flow of the fluid possible.