A remedial unit in a vehicle antitheft device capable of performing starting control according to an authentication result derived from radio communication between a portable unit and an onboard unit, with great security regarding permission to start the vehicle when the portable unit cannot be used, the onboard unit including: a unit detecting that terminals of a predetermined electric wiring outside the onboard unit are connected by a connecting element; a unit detecting a predetermined signal indicating that a key cylinder outside the onboard unit is at a predetermined position; a unit detecting a signal generated by a password manual entry switch outside the onboard unit; and a unit generating a starting control command to a vehicle drive control unit when a predetermined password is entered after conductiveness of the electric wiring and occupation of the predetermined position by the mechanical key have been detected by the units.