An airbag for a front passenger's seat internally includes a communication port defined by an inner joint that joins inner circumferential edges of a pair of inner panels. The airbag includes at a rear side a recess and a pair of raised regions. The airbag further includes a contact portion where outer surfaces of the inner panels are in face-to-face contact proximate the circumference of the communication port at full inflation. The contact portion is created and maintained by an inner pressure of the airbag at full inflation that acts on the panels of the airbag, and is not formed if the inner pressure is less than that at full inflation of the airbag.