To efficiently execute setting work and changing work for a material set frame by providing an engagement member removably engaged with an engagement part by energizing force of an elastic energizing member in the material set frame, and moving the engagement member against the energizing force of the elastic energizing member to release the engagement with the engagement part.

A material set frame is provided with a frame removing means. The frame removing means is provided with an engagement member (flapper) 20 removably engaged with an engagement part (flapper receiving part) 28 by energizing force of a spring member 21 which is an elastic energizing member. Further, the apparatus is provided with an engagement releasing means adapted to move the flapper member 20 against the energizing force of the spring member 21 to release the flapper 20 with the flapper receiving part 28. In the engagement releasing means, by a hook 31 as a reversing means, a reversing member 17 is forcedly reversed to draw in a holding rod member 19 against the energizing force of the spring member through a link means K, thereby putting the flapper 20 in the retreat position.