A roof air bag apparatus for a vehicle includes a roof air bag cushion protecting a passenger, and the roof air bag cushion can be separated into a front air bag cushion and a rear air bag cushion. In particular, the front air bag cushion and the rear air bag cushion are unfolded into a space between a front passenger and a rear passenger in a face-to-face mode at the time of occurrence of a car accident, such that the unfolded front air bag cushion protects the front passenger by absorbing an impact force, and the unfolded rear air bag cushion protects the rear passenger by absorbing an impact force.