A sanitary napkin that is provided with large rear flaps to effectively prevent liquid from leaking obliquely rearward. The rear flaps are disposed rearward of fold-back flaps to be wrapped around a crotch part of an undergarment. The rear flap is of a shape spreading rearwardly from a starting point. With a pressure from the thighs acting forward of the starting point, leakage preventing walls forward of the starting point can be maintained in a rising state during wear. On the other hand, the leakage preventing walls rearward of the starting point may possibly fall outward. However, even if the leakage preventing walls fall outward rearward of the starting point, they will never project out of the rear flaps. Accordingly, they hardly leave a stain on an undergarment.