A portable bacteria detector not only simply capable of inspecting the presence of food-poisoning bacteria and the like but also provided with a disinfecting or sterilizing means itself has been widely used. As its application fields spread, the detector has been required to be more inexpensive and be constituted in a form allowing easier waste disposal. In a portable bacteria detector provided with a culture medium and a disinfectant or germicide, constituent members for the detector are formed of plastic materials which are easy to incinerate. Furthermore, once a sample has been collected and a process for detecting the presence of bacteria has been started, the detector can be operated in a completely closed system. In this bacteria detector, an external force is applied from a direction perpendicular to the axis of the detector to break off a fragile part inside the detector, thereby leading to the performance of a liquid chamber opening operation.