A treatment instrument for endoscopes includes a sheath, an operation wire, an operation unit, a treatment unit support member having a tube part and a pair of arm parts, treatment pieces, a pair of driving links, and a forward and backward movement transmission rod. The treatment unit support member forms treatment liquid supply paths between the arm parts and the treatment pieces by two concave surface parts formed on inner surface of the arm parts. An inner concave wall having a through hole passing through and guiding the forward and backward movement transmission rod is formed in the tube part. The concave surface parts form the treatment liquid supply path by a pair of liquid supply parts in the through hole. An opening and closing degree of the treatment piece is restricted by a stopper of the arm part and a stopper of the tube part.