A sensor for detecting a specific object (such as a hand) excellent in operation reliability and response, further excellent in mountability (dominance such as in size and design) on a vehicle, and much less in power consumption than conventional impulse radars. The object sensor comprises detecting wave transmitting means and reflected wave receiving means of an impulse radar and a judging circuit part (40) for turning on the detection output when the amplitude level of a signal component, in a frequency range corresponding to the moving speed range of a specific object, of a signal received by the reflected wave receiving means lies in a predetermined range corresponding to the reflection characteristics of the specific object.