A remote start-up control apparatus which takes in a key code outputted on the basis of insertion of a key cylinder of an ignition key, and which is mounted on a vehicle which was equipped with an immobilizer unit for enabling a start-up of an engine, in case that it was judged that the taken-in key code is in conformity with a predetermined key code, and which carries out start-up control of an engine in response to an instruction of a portable transmitter, has a unit for supplying a key code which has been stored in an EEPROM to the immobilizer, when it received a start-up instruction of the engine according to a remote operation, and a unit for prohibiting supply of the key code, in case that there occurred vehicle theft.