To provide a device for determining the degradation of engine oil that can accurately determine the degradation of the engine oil, and appropriately gives a driver or the like the exchange timing of the engine oil.

An integrated value of a pentane insoluble portion is obtained to determine oil degradation (steps ST3 to ST6) based on a pentane insoluble portion map in view of mutual action between respective parameters of engine rotation speed Ne, a load Tq, an oil temperature Temp. In this manner, it becomes possible to determine accurately oil degradation by using the pentane insoluble portion map with consideration given to the mutual action of a plurality of parameters including the engine rotation speed Ne, the load Tq, the oil temperature Temp, rather than calculating a degradation index for each parameter of the engine rotation speed Ne, the load Tq, the oil temperature Temp, and to properly inform a driver or the like of the exchange timing of engine oil.