Waste heat recovering apparatus for an engine

The absence or shortage of a heat transfer medium can be detected without any time lag. While the medium is circulated through a water jacket (6A) and an exhaust gas heat exchanger (9) which receives heat from the exhaust gas, the heat generated by the engine (2) can be recovered. A first sensor (TW1) is provided at a waste heat recovering location in a circulation path (12) of the medium. A second sensor (TW2) is provided at the downstream of the sensor (TW1). When the medium is absent, there is developed a difference in the temperature measurement between the sensor (TW1) and the sensor (TW2) which is greater than a reference level. A heat transfer medium shortage signal (D) is outputted when a difference ( DELTA T) in the temperature measurement between the first sensor (TW1) and the second sensor (TW2) exceeds the reference level ( DELTA Tref).