a shield mounting structure is disclosed wherein base plates each having a pivot shaft serve as a pivoting center of a shield and also have a stopper mechanism for restricting a pivoting range of the shield and are provided on both right and left sides of a helmet body , and the shield adapted to rotate about the said pivot shaft to effect opening and closing motions is prevented from dislodgement by means of a shield keep cover provided axially outwards of the pivot shaft and having resilience . inclined faces for pushing up the shield axially outwards along the axis of the pivot shaft and that of the stopper mechanism are formed on constituent members provided on the base plate , and an opening which permits insertion and removal therethrough of each of mounting portions of the shield is formed between the front edge of the shield keep cover and the outer surface of the helmet body , whereby the mounting and removal of the shield can be done through the said opening while the shield keep cover is left engaged with the helmet body or the base plate .