Seatbelt assist device and vehicle seat

A method for manufacturing a vehicle seat, wherein the vehicle seat has a support portion configured to support a back of a seated passenger from behind the back of the seated passenger and a lateral portion positioned at a side of the support portion and an airbag module, the lateral portion has a resin plate and a cover material, the resin plate has a space formation portion and a recessed airbag housing portion that is disposed at a different position from the space formation portion, the space formation portion includes a bottom wall portion and side wall portions provided respectively on both sides of the bottom wall portion, the method comprising:

• preparing the resin plate;
• housing the airbag module in the recessed airbag housing portion that formed on the resin plate;
• and
• covering the resin plate and the airbag module by the cover material;
• wherein at least a portion of the space formation portion opposes a belt portion of a seatbelt when a seatbelt is at a standby position in an unlocked state,
• wherein at least a portion of the space formation portion is formed on a side of the support portion with respect to the airbag module, and
• wherein the side wall portion of the space formation portion that is positioned on the side of the support portion with respect to the airbag module is positioned closer to the support portion in a width direction of the vehicle seat than a side wall portion of the recessed airbag housing portion that is positioned on the side of the support portion with respect to the airbag module.