Abstract: A biomolecule detecting element capable of easily immobilizing a detecting probe and being used in a simple manner without requiring a dark box and the like. A biomolecule detecting probe is immobilized on the surface of a conductive electrode of an insulated gate field effect transistor, the conductive electrode being formed on the surface of a gate insulating material between a source and a drain. Portions other than the conductive electrode are covered with a light-shielding member so as to eliminate the influence of light. During measurement, the conductive electrode having a biomolecule detecting probe immobilized on the surface thereof and a reference electrode are disposed in a buffer solution in a measurement cell.