A microorganism testing device includes a measurement chip having a specimen container; a reaction container for mixing a specimen and a dyeing reagent; a bacteria detection portion irradiated with excitation light; a detection liquid waste container a solution flow path which connects the specimen container, the reaction container and the bacteria detection portion, and ventilation ports which are connected to the specimen container, the reaction container and the detection liquid waste container, through a air flow path and is connected to a chip connecting tube. Bacteria are detected in the bacteria detection portion by switching of the states of the containers between a sealed state and a state open to the atmospheric pressure, by moving the specimen to the reaction container to mix and stir the specimen and the dyeing reagent, and by moving of the liquid mixture to the detection liquid waste container.