<p>Leakage or the like is accurately detected based on a pressure and a flow volume obtained while a fluid is used. The flow volume of a gas flowing in a channel (102) is measured by a flow volume measuring section (106), and the pressure is measured by a pressure measuring section (108). An analyzing section (112) inputs measured flow volume data and pressure data and analyzes a flow volume change with respect to a pressure change. A flow volume change quantity of a prescribed quantity or more with respect to a pressure change quantity is classified into a plurality of ranges by prescribed threshold values, and based on judgment conditions for each range of the flow volume change quantity, the flow volume quantity change with respect to the pressure change is judged.</p>
