There is provided an airbag in which there are fewer restrictions in a place for setting a tension member and a place for setting a vent hole. Airbag (10) of the present invention has bag-shaped airbag main body (20), tension member (30, 30a, 30b) disposed inside airbag main body (20), and vent hole (50) provided in airbag main body (20). In two-dimensional view in which an inner side of inflated and deployed airbag main body (20) is viewed from a direction orthogonal to vent hole (50) via vent hole (50), tension member (30, 30a, 30b) has overlapping portion (35) disposed at a position overlapping vent hole (50), and a dimension of at least a part of overlapping portion (35) in an orthogonal direction is smaller than a gap of a portion of vent hole (50), which corresponds to overlapping portion (35), in the orthogonal direction.