A fuel property detection apparatus detects fuel properties based on cetane number and density of a tested fuel. Tested fuel is examined in terms of ignition timing, and, when the tested fuel has an ignition timing earlier than a threshold, the tested fuel is identified as having a standard cetane number. When the tested fuel has an ignition timing later than the threshold, the tested fuel is identified as having a low cetane number. An advance angle of the ignition timing is increased for yielding a greater ignition timing difference between a light property fuel and a heavy property fuel, and, in such manner, the difference therebetween is detected. When an advancement of the ignition timing is greater than a threshold, the fuel property is identified as heavy, and, when an advancement of the ignition timing is smaller than the threshold, the fuel property is identified as light.