A handling device of security data of a vehicle includes: an in-vehicle unit having a portable unit authenticating unit, an EEPROM, a ROM, and a controller; a vehicle having the in-vehicle unit, a door locking mechanism, and a communication unit; and a portable unit for locking or unlocking the door locking mechanism of the vehicle. In the above device, an encryption unit for encrypting the security data with a cipher key is interposed between the controller and the EEPROM, the security data is encrypted with the cipher key and stored into the EEPROM, according to the instruction from the controller based on the authentication result of the portable unit authenticating unit, and the cipher key is stored into the ROM.