To provide a clincher device capable of forming a flat stapling form and being used for a manual stapler having no driving source.

This clincher device 3 is constituted of a clincher member 10 having a guide surface 11 for bending and guiding a staple leg L inward on an upper end surface, and a metal thin plate piece 12 arranged so as to cover an upper part of the guide surface 11 of the clincher member 10. A guide space 18 for guiding the staple leg L almost in parallel to the back surface of binding paper P is formed between the guide surface 11 and the thin plate piece 12, and the staple leg L penetrating the binding paper P is bent along the guide space 18.