A vehicle body structure, comprising: a pair of side components that are provided on left and right sides of a vehicle body and form side portions of the vehicle body; and a roof component including a roof arch disposed between the paired side components; and a roof panel fitted to an upper portion of the roof arch and forming an upper surface of the vehicle body; wherein the side components each include a roof side rail disposed at an upper side edge of the vehicle body and extending in a front or rear direction, wherein the roof side rail includes a mount portion extending inward in the vehicle-transversal direction and having a vehicle-transversally outer end portion of the roof panel mounted thereto, wherein the roof arch includes a vehicle-transversally outer end portion that is located outside a vehicle-transversally inner end of the mount portion in the vehicle-transversal direction and is joined with the roof side rail, wherein the vehicle-transversally outer end portion of the roof arch is disposed at a position that is spaced apart downward from the vehicle-transversally outer end portion of the roof panel, wherein at least one of the roof arch and the roof side rail includes a flange portion (24, 25, 43) that extends toward the other one of the roof arch and the roof side rail and comes into contact with said other one of the roof arch and the roof side rail to restrict downward movement of the roof arch, characterized in that the flange portion (24, 25, 43) is located at a position upwards of the vehicle-transversally outer end portion of the roof arch, that the mount portion is located between the roof panel and the roof arch with said other one of the roof arch and the roof side rail being in contact with the flange portion (24, 25, 43), and that the mount portion has the vehicle-transversally outer end portion of the roof panel mounted thereon. a pair of side components that are provided on left and right sides of a vehicle body and form side portions of the vehicle body; and a roof component including a roof arch disposed between the paired side components; and a roof panel fitted to an upper portion of the roof arch and forming an upper surface of the vehicle body; wherein the side components each include a roof side rail disposed at an upper side edge of the vehicle body and extending in a front or rear direction, wherein the roof side rail includes a mount portion extending inward in the vehicle-transversal direction and having a vehicle-transversally outer end portion of the roof panel mounted thereto, wherein the roof arch includes a vehicle-transversally outer end portion that is located outside a vehicle-transversally inner end of the mount portion in the vehicle-transversal direction and is joined with the roof side rail, wherein the vehicle-transversally outer end portion of the roof arch is disposed at a position that is spaced apart downward from the vehicle-transversally outer end portion of the roof panel, wherein at least one of the roof arch and the roof side rail includes a flange portion (24, 25, 43) that extends toward the other one of the roof arch and the roof side rail and comes into contact with said other one of the roof arch and the roof side rail to restrict downward movement of the roof arch, characterized in that the flange portion (24, 25, 43) is located at a position upwards of the vehicle-transversally outer end portion of the roof arch, that the mount portion is located between the roof panel and the roof arch with said other one of the roof arch and the roof side rail being in contact with the flange portion (24, 25, 43), and that the mount portion has the vehicle-transversally outer end portion of the roof panel mounted thereon.