A mechanism for introducing pressurized air into an extracting cartridge comprises an air pump, an on-off valve, and a pressure sensor for detecting an internal pressure within the extracting cartridge. The on-off valve is turned on in order to introduce the pressurized air into the extracting cartridge. When the internal pressure detected by the pressure sensor has become equal to a predetermined pressure range for a pressurization upper limit, the on-off valve is turned off in order to confine the area within the extracting cartridge in the pressurized state, the pressure being thereby exerted upon a sample liquid, a washing liquid, or a recovery liquid having been injected into the extracting cartridge.