A blood analyzer that can check whether a cap is in place or not and can set a mixing mode at the same time when the specimen container is inserted. A specimen container holder holds a specimen container. A holder driving part can rotatably drive the specimen container holder around an axis arranged in a generally horizontal direction. A gradient angle detecting part detects a gradient angle of the specimen container in the specimen container holder, and a control unit controls the holder driving. The control unit receives an angle detecting signal from the gradient angle detecting part, judges whether or not a blood specimen in the specimen container is to be mixed in accordance with the gradient angle and accordingly controls the holder driving part.