An organism testing apparatus adapted to measure the organisms in a specimen in stable fashion is disclosed in which the organisms are stained, the specimen is concentrated and the information on the organisms contained in the specimen are acquired through a simple process. The apparatus includes a staining unit for staining the organisms having live cells existing in a flowing liquid specimen, a concentration unit for concentrating the organisms in a flowing stained specimen, an individual measuring unit for acquiring the image information on the individuals containing the organisms in the concentrated specimen, and a control unit for measuring the organisms based on the image information on the individuals output from the individual measuring unit.