A door courtesy switch abnormality detection apparatus used in an on-vehicle system in which a door unlocked status is formed based on a wireless signal transmitted from an electronic key is disclosed. The apparatus is configured to generate information representing an abnormality in the door courtesy switch, if the electronic key in a cabin of a vehicle is detected by a antenna having the detection area thereof within the cabin of the vehicle in a situation where an ON/OFF signal of the door courtesy switch is not inverted after the door unlock operation is detected.