clockwise to prevent the bound of the rear blade operating arm 20 that the pin 20b is also a connecting pin with the rear blade group b and that in case the rear blade driving arm 26 is rotated clockwise by the shutter cocking operation the brake lever 37 will be rotated counterclockwise by a pin 41a erected on a lever 41 and will be thereby separated from the pin 20b in this embodiment too the same respective reference numerals are attached to the same component parts and portions in the function as shown in fig3 a that is to say when the rear blade operating arm 20 is rotated clockwise from the illustrated position just before the pin 20b collides with the side of the rear blade driving arm 26 said pin 20b will engage with the side 37a of the brake lever 37 and will rotate the brake lever 37 clockwise with this clockwise rotation of the brake lever 37 the other side 37b will advance into the motion track of the pin 20b and thereby the bound of the rear blade operating arm 20 will be perfectly prevented the lever 41 is pivoted on the base plate p has the pin 41a engageable with the brake lever 37 and is so arranged as to be able to be rotated clockwise from the illustrated position by the shutter cocking operation therefore when the shutter is cocked just before the rear blade driving arm 26 begins to rotate clockwise the brake lever 37 will be rotated counterclockwise by the pin 41a so as to be separated from the pin 20b the other operations are the same as in the embodiment shown in fig3 a and therefore shall not be explained.