To provide a control valve for a variable displacement compressor, which is capable of stably operating in a pressure control area, and causing the compressor to quickly shift to operation with the minimum displacement. The control system comprises a first section which receives first and second gear change instructions which are issued in succession. A front strap forms a loop for securing to a vehicle console. The reaction between the biological sample and the reagents is read from a spectrographic image of the reagent-containing surface obtained by optical methods.