Pretreatment of residual food removal and bacteria dyeing, and measurement of the number of bacteria using the fluorescence flow cytometry method, are stably performed by easy operations. A measurement chip 10 includes: a specimen container 151; a reaction container 170 for mixing a specimen and a dyeing reagent into a liquid mixture; a bacteria detection portion 18 being irradiated with excitation light; a detection liquid waste container 163 into which liquid mixture which has passed the bacteria detection portion enters; a solution flow path 157 which connects the specimen container, the reaction container and the bacteria detection portion, and ventilation ports 1631 through 1633 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 18 by switching of the states of the specimen container, the reaction container, and the detection liquid waste container between a sealed state and a state open to the atmospheric pressure, by moving the specimen to the reaction container 170 to mix and stir the specimen and the dyeing reagent, and by moving of the liquid mixture to the detection liquid waste container 163.