A biologically-relevant substance assay system is disclosed. In a disclosed embodiment, the system comprises (a) a specimen holding portion in which a specimen is held; (b) a first holding portion in which trapping particles for trapping a biologically-relevant substance from the specimen are held; (c) a second holding portion in which a reagent for detecting the biologically-relevant substance is held; and (d) a dispensing mechanism for dispensing the specimen into the specimen holding portion, a mechanism for mixing the specimen with the trapping particles to extract the biologically-relevant substance from the specimen, and a mechanism for mixing the extracted biologically-relevant substance with the reagent for detecting; wherein the specimen holding portion, the first holding portion, and the second holding portion are arranged in an approximate straight line.