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.