An airbag capable of starting a tearing operation of a line-shaped connecting portion on an outer periphery side after entire line-shaped connecting portion on an inner periphery side is torn, and an airbag apparatus provided with the airbag. Each of halfway portions disposed halfway between respective center portion and peripheral edge portion in a front panel 12 and a rear panel 14 is disconnectably connected by means of line-shaped connecting portions 22, 24, and 26. At a halfway portion in an extending direction of each of the line-shaped connecting portions 22, 24, and 26, communicating portions 23, 25, and 27 serving as starting points of the tearing operations therefor are formed. Each of the communicating portions 23 and 25 of the respective line-shaped connecting portions 22 and 24 provided next to each other in a radial direction, and each of the communicating portions 25 and 27 of the respective line-shaped connecting portions 24 and 26 are positioned on opposite sides while sandwiching a center of an airbag 10, respectively.