Airbag, airbag apparatus, and vehicle

To provide an airbag and an airbag apparatus which can absorb an impact to be applied to an occupant sufficiently, an airbag (10) includes a right airbag section (12) to be inflated at the right side ahead of the occupant, a left airbag section (14) to be inflated at the left side ahead of the occupant, and a rear chamber (16) communicating between the base ends of the right airbag section (12) and the left airbag section (14). In a state in which the airbag (10) is inflated, an extending member such as a tie panel does not exist between the tip portions of the right airbag section (12) and the left airbag section (14), and a space (13) formed between the tip portions of the bags (12, 14) opens toward the occupant. The left airbag section (14) has a larger capacity having a larger lateral width in the inflated state.