An analyzing cartridge and method for using it to analyze a sample having a plurality of reservoirs and capillaries connected for communication between these reservoirs and is provided therein with a reagent required for analysis. The reservoirs are provided with openings leading to the outside of the cartridge, and the openings are covered with vents each consisting of a gas-permeable/non-liquid-permeable, hydrophobic, porous membrane. The analyzing cartridge requires only trace amounts of a sample and a reagent and no maintenance. It is provided with a non-fluid reagent in vent-carrying reservoirs thereby making it possible to formulate a very trace amount of reagent solution in the cartridge by injecting a reagent dissolving liquid into the reservoirs immediately before analyzing. A liquid feed control device controls the feeding of the liquid between the reservoirs via the capillaries when it is attached to the cartridge to allow or control the entry/exit of air via the vents.