A weatherstrip comprising: an attachment portion attached to a body of a vehicle; a lip-like flexible seal wall connected to the attachment portion to seal a clearance between a peripheral portion of a roof panel that is replaceable with a roof panel with a different thickness and covers an opening in an upper portion of the vehicle and a peripheral portion of a rear door panel, a lower surface of the peripheral portion of the roof panel and a lower surface of the peripheral portion of the rear door panel contacting a halfway portion of the lip-like flexible seal wall from above; a flexible bridging wall bridging the attachment portion and a lower surface of the seal wall; and a hollow portion surrounded by the attachment portion, the seal wall, and the bridging wall, wherein a retainer extending along the clearance, and a body frame separated from the retainer toward a front of the vehicle by a predetermined distance and extending in a vehicle width direction are arranged below the roof panel in the vehicle, characterised in that the attachment portion includes a front wall located toward the front of the vehicle and a rear wall located toward a rear of the vehicle, has a U-shaped cross-sectional shape that is open downward, and is fitted, from above, to the retainer, the seal wall has a J-shaped cross section, extends from an upper portion of the front wall located inside the vehicle toward a front of a cabin, is then turned up, and extends backwardly of the cabin, an extending end of the seal wall is spaced apart from the attachment portion, and a root portion of the seal wall connected to the attachment portion is made of a material having greater rigidity than a portion of the seal wall except the root portion, and an upper end of the bridging wall is connected to the halfway portion of the seal wall corresponding to the clearance or a portion of the vehicle around the opening in the upper portion of the vehicle. an attachment portion attached to a body of a vehicle; a lip-like flexible seal wall connected to the attachment portion to seal a clearance between a peripheral portion of a roof panel that is replaceable with a roof panel with a different thickness and covers an opening in an upper portion of the vehicle and a peripheral portion of a rear door panel, a lower surface of the peripheral portion of the roof panel and a lower surface of the peripheral portion of the rear door panel contacting a halfway portion of the lip-like flexible seal wall from above; a flexible bridging wall bridging the attachment portion and a lower surface of the seal wall; and a hollow portion surrounded by the attachment portion, the seal wall, and the bridging wall, wherein a retainer extending along the clearance, and a body frame separated from the retainer toward a front of the vehicle by a predetermined distance and extending in a vehicle width direction are arranged below the roof panel in the vehicle, characterised in that the attachment portion includes a front wall located toward the front of the vehicle and a rear wall located toward a rear of the vehicle, has a U-shaped cross-sectional shape that is open downward, and is fitted, from above, to the retainer, the seal wall has a J-shaped cross section, extends from an upper portion of the front wall located inside the vehicle toward a front of a cabin, is then turned up, and extends backwardly of the cabin, an extending end of the seal wall is spaced apart from the attachment portion, and a root portion of the seal wall connected to the attachment portion is made of a material having greater rigidity than a portion of the seal wall except the root portion, and an upper end of the bridging wall is connected to the halfway portion of the seal wall corresponding to the clearance or a portion of the vehicle around the opening in the upper portion of the vehicle.