Accurate positioning of a one dimensional measuring unit in a measuring apparatus that utilizes evanescent waves is enabled. The one dimensional measuring unit is constituted by: a transparent elongate dielectric block; a thin film layer, formed on a flat surface of the dielectric block; and a flow path forming member, which is in close contact with the thin film layer of the dielectric block, for forming a plurality of flow paths in the longitudinal direction of the dielectric block on the thin film layer, with intervals therebetween. A linear guide groove for conveyance is formed in the bottom surface of the dielectric block in the longitudinal direction thereof, and positioning abutment surfaces are formed on the side surfaces and a first end surface of the dielectric block, to accurately position the measuring unit in the X, Y, and Z directions.