To provide an apparatus for cutting out a cutout section from the wall section of a component member formed as a hollow body, while a component member is manufactured based on an internal high tension forming method.

A punch 8 is provided with at least one elastic element at fixing state on the end section 13 in the side departed from a component member 7, and comes contact with the wall section corresponding to the cutout section 6 of the component member 7 at the other end section 11 and the elastic element based on its stiffness constitutes counter pressure against internal pressure as it increases inside the component member 7 and suddenly deforms elastically at the time of exceeding the maximum internal pressure. Accordingly the elastic element is so designed to enable the retreat movement of the punch 8.