A vehicle state monitoring device, comprising: a storage device configured to store information relating to a vehicle traveling under power from an engine; a determining device configured to determine a state of the vehicle using the information stored in the storage device; and a storage control device, wherein the storage control device is configured to, each time the vehicle travels a predetermined distance, store a frequency relation as the information in the storage device, characterized in that the frequency relation being a relation between revolutions (Ne) of the engine, a fuel-related parameter that is a load factor or a fuel injection rate of the engine, and a running frequency (Fr1,Fr2) of the engine at the revolutions and the fuel-related parameter while the vehicle travels the predetermined distance, wherein the storage control device is configured to, each time the vehicle travels the predetermined distance, store a vehicle speed relation in the storage device, the vehicle speed relation being a relation between the revolutions (Ne), the fuel-related parameter, and an average value of a vehicle speed of the vehicle when the engine is running at the revolutions and the fuel-related parameter; and the determining device is configured to determine, when overheating of the engine occurs, a cause of the overheating, using the frequency relation and the vehicle speed relation, wherein a determination is made regarding whether the average value of a vehicle speed is smaller than a first threshold value (Vref2) and whether the running frequency exceeds a second threshold value (Fref2), and when the average value of the vehicle speed is smaller than the first threshold value (Vref2) and when the running frequency exceeds the second threshold value (Fref2), determination is made that the cause of overheating is overloading. a storage device configured to store information relating to a vehicle traveling under power from an engine; a determining device configured to determine a state of the vehicle using the information stored in the storage device; and a storage control device, wherein the storage control device is configured to, each time the vehicle travels a predetermined distance, store a frequency relation as the information in the storage device, characterized in that the frequency relation being a relation between revolutions (Ne) of the engine, a fuel-related parameter that is a load factor or a fuel injection rate of the engine, and a running frequency (Fr1,Fr2) of the engine at the revolutions and the fuel-related parameter while the vehicle travels the predetermined distance, wherein the storage control device is configured to, each time the vehicle travels the predetermined distance, store a vehicle speed relation in the storage device, the vehicle speed relation being a relation between the revolutions (Ne), the fuel-related parameter, and an average value of a vehicle speed of the vehicle when the engine is running at the revolutions and the fuel-related parameter; and the determining device is configured to determine, when overheating of the engine occurs, a cause of the overheating, using the frequency relation and the vehicle speed relation, wherein a determination is made regarding whether the average value of a vehicle speed is smaller than a first threshold value (Vref2) and whether the running frequency exceeds a second threshold value (Fref2), and when the average value of the vehicle speed is smaller than the first threshold value (Vref2) and when the running frequency exceeds the second threshold value (Fref2), determination is made that the cause of overheating is overloading.