This instrument detects whether there is leakage and the rate of the leakage flow of the object (product) under test by filling the object (product) with compressed air at a specified pressure and keeping it pressurized, and by measuring the change of the flow rate on the flow sensor. First of all, the leak detector is filled with pressurized gas to the test object and kept inflated, through the collection of high sensitivity flow sensor data, it senses the change of gas flow caused by leakage, that is, the leakage flow of the test object.