In this study, a biological reaction and measurement control system was developed to rapidly measure the insecticide imidacloprid residues in agricultural products. The biological reaction part of the system was designed to include micro-pumps and valves for fluid transport, and a polystyrene covet as a reaction chamber. The measurement control part of the system consisted of a photodiode with a light-emitting diode for optical density measurement, and a control microcomputer to implement assay. Signal output was read as the rate of change in optical density at 645 nm. The sensitivity of the system was 2.2 ng/mL ($IC_50$). The system could execute a measurement cycle in about 19 minutes. Research will be continued to develop an automatic sampler fur imidacloprid residues from agricultural products.