A vehicular opening/closing body control device includes: a braking control unit configured to apply a braking force to an opening/closing body provided in an opening in a vehicle; a position detection unit configured to detect an opening/closing operation position of the opening/closing body; and a traveling state determination unit configured to determine a traveling state of the vehicle, wherein the opening/closing body is opened/closed along a movement path, which is formed by a guide rail and a guide roller engaged with the guide rail, the guide rail includes a curved portion, which is curved in a width direction of the vehicle, and the braking control unit executes braking control in a case where the opening/closing operation position of the opening/closing body is within a specific range, which is set in the movement path of the opening/closing body to correspond to the curved portion of the guide rail.