A method of inspecting a leak detection system in a short time is disclosed. The leak detection system includes a leak detection line, an on-off valve, a flow mater, an operation controller configured to detect a fluid leak from a fluid line based on a first flow rate measured by the flow mater, a drain line, and a drain valve attached to the drain line. The inspection method includes: opening the on-off valve and the drain valve, with a supply valve and a return valve closed; measuring a second flow rate of fluid in the leak detection line by the flow mater; and determining that the leak detection system has a defect when the second flow rate is lower than a predetermined reference value.