REAR SEAT SIDE AIRBAG DEVICE

A side airbag may be smoothly deployed when there is a side collision, and damage to the side airbag at edges of a module case is prevented or suppressed. A recess portion (36) is formed in a seat frame (28) made of resin, and an airbag module (38) is accommodated in the recess portion (36). The airbag module (38) is provided with a module case (40) in a substantial box shape. An upper side gap (80) is formed between an upper wall portion (40D) and an upper end (42A) of a side airbag (42), and a lower side gap (82) is formed between a lower wall portion (40E) and a lower end (42B) of the side airbag (42). A length (H1) of the upper wall portion (40D) is set shorter than a length (H2) of an upper wall portion (36D) of the recess portion (36). As a result, the side airbag (42), particularly the upper end (42A), is less likely to come into contact with the upper wall portion (40D) of the module case (40).