Support portions (12, 13) are integrally moulded on an inner surface of a helmet shell (4) made of synthetic resin for supporting folded-back portions (8a, 9a) of a chin strap (3), and strap holes (10, 11) through which the chin strap (3) is passed, are provided in a shock-absorbing liner (5) in correspondence to the support portions. Thus, the chin strap (3) can be simply attached to a cap body (2) without use of a separate support plate and rivet, thereby providing a cost reduction and a better external appearance.