To provide a binding needle forming mechanism capable of binding a binding object material by a binding needle like an ordinary stapler, and enabling the binding object material to be easily visible without hiding a character without having a binding margin.

The stapler binds the binding object material by bending its leg part by a needle receiving seat c-1 by driving out the binding needle composed of two leg parts and its connection part by a driving-out mechanism. The stapler is formed so that only one leg part of the binding needle penetrates through the binding object material, and the entire binding needle forms a circular or polygonal annular shape by the driving-out mechanism and the needle receiving seat.