To provide a binder capable of easily binding reinforcements to each other.

The binder used to bind body surfaces of long-sized members such as reinforcements or pipes to each other is provided with a bifurcated holding member 3 having an opening K for inserting the long-sized members inside to hold the long-sized members, and a body 4 having a guide path i and a port 12 for holding the discharged member 3. The member 3 is formed in a U-shape comprising an upper frame 3a, a lower frame 3b and a frame 3c for connecting both upper and lower frames. The port comprises a lower part having a recess for holding the lower frame in a held state, and an upper part having an upper opening R corresponding to the upper frame of the holding member held in the recess. A hammer member 5 is rotatably mounted. The member 3 further has a first engaging part 6 with a first engaging face of a serrated shape at the tip of the upper frame, and a second engaging part 7 with a second engaging face of a serrated shape at the tip of the lower frame so as to be engaged with the first engaging face when the upper frame is pressed to the lower part side by the hammer member to bind the long-sized members.