<p>Provided is an undercap (10) for providing a cap with increased shock resistance similar to that of a helmet. This undercap (10) is formed from a flexible material and is provided with a cap body (12) for covering the head of a human when attached to the inside of a cap and a cushioning member (14) formed on the cap body (12). The cap body (12) is provided with a top part (12A) which accommodates the crown of the head and a periphery part (12B) which is formed so as to extend from the periphery of the top part (12A) and hang downward to cover the parts of the head other than the crown. This periphery part (12B) has multiple slits (16) which divide the periphery part (12B) into multiple parts and allow the multiple divided periphery parts (12B) to overlap or to be separated from one other. The cushioning member (14) comprises multiple hollow cylindrical protrusions (18) which open upward.</p>
