The present invention relates to a unit to be used for detection of interactions of biologically relevant molecules using a carrier on which the biologically relevant molecules are immobilized, comprising: a hollow holder having an open part at one end with the other end being closed; and a carrier-supporting member that can be inserted into the hollow holder, on which is mounted a carrier upon which biologically relevant molecules are immobilized, wherein: while the carrier-supporting member is being inserted into the hollow holder, a rear-end portion of the carrier-supporting member is engaged with an edge of the open part of the hollow holder, so that the hollow holder is sealed and the positions of the carrier-supporting member and the hollow holder are determined; and the area on the left and the area on the right of the axial center, which are defined by the inner side of the hollow holder and the external side of the carrier-supporting member on which the carrier has been mounted, are approximately the same within the region from the carrier-mounting part to the apical part of the carrier-supporting member, as in a section cut along a plane including the axial center of the hollow holder in a positioned state.