An airbag and airbag apparatus in which a venthole is closed or opened by a small amount until an occupant hits the airbag, and the venthole is opened or opened by a large amount when the occupant hits the airbag. Inner panels 22A and 22B are provided inside of an airbag 10. Ventholes 18 and 18A allowing an inside and an outside of the airbag 10 to communicate with each other are provided in a rear panel 14. A lid member 60 for covering the venthole is provided on an outer surface side of the rear panel 14. The venthole 18A is a constantly-open type venthole that is not covered by means of the lid member 60. A tether 70 couples the lid member 60 with the inner panels 22A and 22B through the constantly-open type venthole 18A.