A front passenger seat airbag device, comprising: an airbag cushion that expands and deploys above an instrument panel of a vehicle and between the instrument panel and a front passenger seat in a condition contacting an upper surface of the instrument panel; and an inflator that supplies gas to the airbag cushion, the inflator being secured to an inner side of the instrument panel; wherein the airbag cushion includes: a pair of side panels that form side portions on two sides of the airbag cushion in a vehicle width direction, and a strip-shaped main panel connecting edges of the pair of side panels to each other; the pair of side panels have an acute angle portion that extends along the upper surface of the instrument panel toward the front of the vehicle at an acute angle; and the airbag cushion further includes: an inner seam margin in which an edge of the main panel and edges of the pair of side panels are joined in a condition bent to the inner side of the airbag cushion, and an outer seam margin in which end portions (138a, 138b) on two sides of the main panel in a longitudinal direction are vertically overlapped and joined in a state further extending to the front of the vehicle from the acute angle portion of the pair of side panels. an airbag cushion that expands and deploys above an instrument panel of a vehicle and between the instrument panel and a front passenger seat in a condition contacting an upper surface of the instrument panel; and an inflator that supplies gas to the airbag cushion, the inflator being secured to an inner side of the instrument panel; wherein the airbag cushion includes: a pair of side panels that form side portions on two sides of the airbag cushion in a vehicle width direction, and a strip-shaped main panel connecting edges of the pair of side panels to each other; the pair of side panels have an acute angle portion that extends along the upper surface of the instrument panel toward the front of the vehicle at an acute angle; and the airbag cushion further includes: an inner seam margin in which an edge of the main panel and edges of the pair of side panels are joined in a condition bent to the inner side of the airbag cushion, and an outer seam margin in which end portions (138a, 138b) on two sides of the main panel in a longitudinal direction are vertically overlapped and joined in a state further extending to the front of the vehicle from the acute angle portion of the pair of side panels. a pair of side panels that form side portions on two sides of the airbag cushion in a vehicle width direction, and a strip-shaped main panel connecting edges of the pair of side panels to each other; the pair of side panels have an acute angle portion that extends along the upper surface of the instrument panel toward the front of the vehicle at an acute angle; and the airbag cushion further includes: an inner seam margin in which an edge of the main panel and edges of the pair of side panels are joined in a condition bent to the inner side of the airbag cushion, and an outer seam margin in which end portions (138a, 138b) on two sides of the main panel in a longitudinal direction are vertically overlapped and joined in a state further extending to the front of the vehicle from the acute angle portion of the pair of side panels. an inner seam margin in which an edge of the main panel and edges of the pair of side panels are joined in a condition bent to the inner side of the airbag cushion, and an outer seam margin in which end portions (138a, 138b) on two sides of the main panel in a longitudinal direction are vertically overlapped and joined in a state further extending to the front of the vehicle from the acute angle portion of the pair of side panels.