An object of the present invention is to provide a flow path device capable of suppressing an occurrence of air bubbles when a solution is introduced into a flow path. A fluidic device has a pair of substrates which are stacked in a thickness direction, one substrate including a flow path formed by being covered with the other substrate. The flow path includes a merging/branching portion which is surrounded by a contour which is configured to match each line segment connecting together apex positions of an equilateral triangle as viewed in the thickness direction or a contour parallel to each line segment and in which solution merges or branches. A valve which is configured to regulate flow of a fluid in the flow path is provided in at least two of the apex positions.