A helmet is provided which is to be worn on the head of a helmet wearer and can be removed from the head with a comparatively small force. Operation for removing the helmet, including preliminary operation for it, can be performed easily and quickly.A recess-projection engaging mechanism to attach a blockish inside pad to a head protecting cap portion side includes an engaging pin on the inside pad side or head protecting cap portion side, and a notched engaging hole on the head protecting cap portion side or inside pad side. When pulling the inside pad outward from inside the head protecting cap portion at least partly, the engaging pin moves relative to outside the engaging hole through a notch of the engaging hole.