An optical measurement device for a reaction vessel comprising: a vessel group (20, 120) in which two or more reaction vessels are arranged; a light guide stage (32, 320, 132) having two or more linking portions (31 i, 131 i) to which front ends of one or two or more light guide portions (33 i), which have a flexibility, that are directly or indirectly linkable with said respective reaction vessels and optically connect with the interior of the linked reaction vessels, are provided; wherein the light guide stage (32, 320, 132) comprises a horizontal plate, wherein the light guide portions pass through the horizontal plate and protrude upwards away from the reaction vessels; a connecting end arranging body (30, 300) that has an arranging surface that arranges and supports along a linear path in a first direction two or more connecting ends (34 i), to which back ends of the light guide portions (33 i), in which the front ends thereof are provided to the linking portions (31 i, 131 i), are provided, and the connecting ends (34 i) are provided corresponding to the respective linking portions (31 i, 131 i); a measurement device (40, 400) provided approaching or making contact with said arranging surface that has two or more measuring ends (44 i) that are linearly aligned along a straight line in the first direction and that are successively optically connectable with said respective connecting ends (34 i) along said linear path, and in which light based on an optical state within said reaction vessels is receivable by means of optical connections between the connecting ends (34 i) and the measuring ends (44 j); a light guide switching mechanism that is adapted to relatively move said respective connecting ends (34 i) arranged on said connecting end arranging body (30, 300) and said respective measuring ends (44 j) along the first direction such that they are successively optically connected; a nozzle head (50, 500, 150) having a suction-discharge mechanism that performs suction and discharge of gases, and one or two or more nozzles (71 i) that detachably mount dispensing tips in which the suction and the discharge of liquids is possible by means of the suction-discharge mechanism; and a nozzle head transfer mechanism that makes the nozzle head (50, 500, 150) relatively movable between said vessel groups (20, 120), wherein said light guide stage (32, 320, 132) is provided to the nozzle head (50, 500, 150). a vessel group (20, 120) in which two or more reaction vessels are arranged; a light guide stage (32, 320, 132) having two or more linking portions (31 i, 131 i) to which front ends of one or two or more light guide portions (33 i), which have a flexibility, that are directly or indirectly linkable with said respective reaction vessels and optically connect with the interior of the linked reaction vessels, are provided; wherein the light guide stage (32, 320, 132) comprises a horizontal plate, wherein the light guide portions pass through the horizontal plate and protrude upwards away from the reaction vessels; a connecting end arranging body (30, 300) that has an arranging surface that arranges and supports along a linear path in a first direction two or more connecting ends (34 i), to which back ends of the light guide portions (33 i), in which the front ends thereof are provided to the linking portions (31 i, 131 i), are provided, and the connecting ends (34 i) are provided corresponding to the respective linking portions (31 i, 131 i); a measurement device (40, 400) provided approaching or making contact with said arranging surface that has two or more measuring ends (44 i) that are linearly aligned along a straight line in the first direction and that are successively optically connectable with said respective connecting ends (34 i) along said linear path, and in which light based on an optical state within said reaction vessels is receivable by means of optical connections between the connecting ends (34 i) and the measuring ends (44 j); a light guide switching mechanism that is adapted to relatively move said respective connecting ends (34 i) arranged on said connecting end arranging body (30, 300) and said respective measuring ends (44 j) along the first direction such that they are successively optically connected; a nozzle head (50, 500, 150) having a suction-discharge mechanism that performs suction and discharge of gases, and one or two or more nozzles (71 i) that detachably mount dispensing tips in which the suction and the discharge of liquids is possible by means of the suction-discharge mechanism; and a nozzle head transfer mechanism that makes the nozzle head (50, 500, 150) relatively movable between said vessel groups (20, 120), wherein said light guide stage (32, 320, 132) is provided to the nozzle head (50, 500, 150).