A helmet comprising: supporting shafts that are fixed to outer side surfaces of a helmet main body, and that have outer peripheral surfaces at which a plurality of contact pieces (96A, 96B, 96C) are formed; and a chin guard having proximal end portions at which are formed supporting holes into which the supporting shafts are inserted, and that is mounted so as to be able to rotate around the supporting shafts that are inserted into the supporting holes, between a fully closed position at which the chin guard protects a jaw of a helmet wearer and a fully open position at which the chin guard expands a field of view of the helmet wearer, and at which cam surfaces, having positions of contact with the contact pieces (96A, 96B, 96C) that change accompanying rotation, are formed at inner peripheral surfaces of the supporting holes, characterized in that each cam surface has an anchor surface that, in a case in which the chin guard is rotated to a position immediately before the fully open position, by being abutted by at least one of the contact pieces (96A, 96B, 96C) accompanying rotation, imparts resistance in a direction opposite to a rotating direction of the chin guard, and a concave portion into which, in a case in which the chin guard is rotated past the immediately before the fully open position to the fully open position, at least one of the contact pieces (96A, 96B, 96C) is fit and that fixes the chin guard at the fully open position, and wherein, when the chin guard rotates to the fully open position, the chin guard is fixed due to, with at least one of the contact pieces (96A, 96B, 96C) remaining in a state of abutting the anchor surface of the cam surface, another at least one of the contact pieces (96A, 96B, 96C) being fit in the concave portion. supporting shafts that are fixed to outer side surfaces of a helmet main body, and that have outer peripheral surfaces at which a plurality of contact pieces (96A, 96B, 96C) are formed; and a chin guard having proximal end portions at which are formed supporting holes into which the supporting shafts are inserted, and that is mounted so as to be able to rotate around the supporting shafts that are inserted into the supporting holes, between a fully closed position at which the chin guard protects a jaw of a helmet wearer and a fully open position at which the chin guard expands a field of view of the helmet wearer, and at which cam surfaces, having positions of contact with the contact pieces (96A, 96B, 96C) that change accompanying rotation, are formed at inner peripheral surfaces of the supporting holes, characterized in that each cam surface has an anchor surface that, in a case in which the chin guard is rotated to a position immediately before the fully open position, by being abutted by at least one of the contact pieces (96A, 96B, 96C) accompanying rotation, imparts resistance in a direction opposite to a rotating direction of the chin guard, and a concave portion into which, in a case in which the chin guard is rotated past the immediately before the fully open position to the fully open position, at least one of the contact pieces (96A, 96B, 96C) is fit and that fixes the chin guard at the fully open position, and an anchor surface that, in a case in which the chin guard is rotated to a position immediately before the fully open position, by being abutted by at least one of the contact pieces (96A, 96B, 96C) accompanying rotation, imparts resistance in a direction opposite to a rotating direction of the chin guard, and a concave portion into which, in a case in which the chin guard is rotated past the immediately before the fully open position to the fully open position, at least one of the contact pieces (96A, 96B, 96C) is fit and that fixes the chin guard at the fully open position, and wherein, when the chin guard rotates to the fully open position, the chin guard is fixed due to, with at least one of the contact pieces (96A, 96B, 96C) remaining in a state of abutting the anchor surface of the cam surface, another at least one of the contact pieces (96A, 96B, 96C) being fit in the concave portion.