in an abnormality detection apparatus for vehicle engines , a deceleration discriminating circuit discriminates a deceleration state of a vehicle engine on the basis of a running state of the engine detected by a running state detector for detecting a running state of the vehicle engine . when the deceleration discriminating circuit determines that the engine is being in deceleration state , a comparing circuit compares a vehicle speed detected by a vehicle speed detector with a predetermined value . an abnormality deciding circuit is responsive to a comparison result signal from the comparing circuit to decide abnormality of the vehicle speed detector .