The present invention provides a method for controlling the spatial arrangement of an energy donor and an energy acceptor in a reaction complex in order to carry out the measurement with good precision and high sensitivity, and a measurement system using the method. Two types of material having affinity for the subject material to be measured are respectively labeled with a combination of reporters that give rise to energy transfer; those that have been thus obtained by labeling these materials are each further labeled with materials that have weak affinity for each other to give reagents, which are then mixed with a sample to give the reaction complex. Each of the materials is brought into spatial proximity by binding based on the affinity among the materials having weak affinity for each other in the reaction complex, and since that condition is stably maintained, a more efficient energy transfer occurs.