An airbag apparatus having an airbag, which is formed into a bag shape by sewing a base fabric, is disclosed. The airbag includes a seam having a first seam section and a second seam section, which is formed after the first seam section is formed. The second seam section has an extremity and an overlapped portion, which is a section between the extremity and an intersected portion. The first seam section has an end part, which includes an overlapping portion. The overlapping portion is located at a position inside of the overlapped portion of the second seam section and extends along the overlapped portion. The overlapping portion includes an intersecting portion, which intersects the intersected portion of the second seam section. The end part of the first seam section further includes an extension, which extends from the intersecting portion to a position that is outside of the second seam section.