in the reactor plate 1 is designed so that the liquid tightness of the reaction well 5 is maintained in a state where there is no difference between the pressure in the injection channel 17 and the pressure in the reaction well 5 the reaction well air vent channel 19 is also designed so that the liquid tightness of the reaction well 5 is maintained in a state where there is no difference between the pressure in the reaction well 5 and the pressure in the reaction well air vent channel 19 the main channel 13 constituting the reaction well channel the liquid drain space 29 connected to the main channel 13 and the drain space air vent channel 23 can be hermetically sealed by switching of the switching valve 63 the wells 35 37 and 39 are sealed with the septum 41 or the film 47 the channels 35 a 35 b 37 a 37 b 39 a and 39 b connected to the wells 35 37 and 39 respectively can be hermetically sealed by switching the switching valve 63 one end of the air vent channel 53 b is connected to the bellows 53 and therefore the air vent channel 53 b is hermetically sealed as described above the wells and channels in the reactor plate 1 constitute a closed system it is noted that even in a case where the reactor plate.