To improve convenience of a sensor unit using a transistor in analysis, a sensing gate for detection 117 of a sensor unit for detecting a detection target comprises a transistor part 103 having a substrate 108, a source electrode 111 and a drain electrode 112 provided on the substrate 108, a channel 113 forming a current path between the source electrode 111 and the drain electrode 112, and the sensing gate for detection 117 is provided with a gate body 115 fixed to the substrate 108 and a sensing part 116 capable of electrically conducting to the gate body 115 and on which a specific substance 123 capable of selectively interacting with the detection target is immobilized.