NOVELTY - The device has a reservoir configured to supplement coolant in thermal management system, connected to the upper end of a radiator (12), and a pressure sensor (20) mounted on a coolant circulation line connected to an inlet of the fuel cell stack (10) which discharges coolant to the radiator. When the pressure sensor measures flow pressure of coolant in real time and transmits measured value to a controller, the controller determines whether the coolant is insufficient based on a change in slope value and a change in amplitude of flow pressure of coolant.    USE - Device for detecting coolant level in thermal management system of fuel cell vehicle. Can also be used in motor vehicles such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, etc.    ADVANTAGE - The device accurately and rapidly detects the lack of coolant using a detection value of a pressure sensor. The lack of coolant can be monitored accurately and rapidly by calculating in real time the lack of coolant based on a change in slope value and a change in amplitude of a detection value of a pressure sensor. The flow noise of coolant and the evaporation amount of coolant can be reduced. The coolant level sensor in the reservoir can be eliminated, and thus the packaging is more efficient and the manufacturing costs are reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for detecting coolant level in thermal management system of fuel cell vehicle.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the device for detecting the coolant level in a thermal management system of fuel cell vehicle. (Drawing includes non-English language text)    Fuel cell stack (10)    Radiator (12)    Three-way valve (13)    Pressure sensor (20)    Pressure cap (22)