A device for detecting leakage of liquid in a tank, capable of detecting the leakage at high accuracy and sensitivity for a wide range of a leakage quantity. A flow rate sensor section attached to a measurement fine tube (13b) includes temperature sensors (133, 134) and an indirectly heated sensor (135). A leakage detection control section connected to a pressure sensor (137) for measuring a liquid level and to the flow rate sensor section has a voltage generation circuit (67) for applying a voltage to a heater (163) of the indirectly heated sensor, a first leakage detection circuit (71), and a second leakage detection circuit for generating an output corresponding to temperature sensed by the indirectly heated sensor (135). First leakage detection using an output of the first leakage detection circuit, second leakage detection using an output of the pressure sensor, and third leakage detection using an output of the second leakage detection circuit are performed, and at least one of the results of the detections is outputted.