A mechanical arresting disk brake comprising: an adjustment bolt mounted on an action part side of a calliper body; a piston provided at a tip of said adjustment bolt; and action part side as well as reaction part side friction pads (6,7) that are adapted to be brought, by a movement of said piston toward a disk rotor, into sliding contact with both side faces of the disk rotor; wherein the adjustment bolt and the piston are formed integrally, and wherein a tip of the piston is fittingly arranged, characterised by a C-clip intervening, on a circular coupling section formed on a backing plate that constitutes a back side of the friction pad (6,7), to connect the friction pad (6,7) and the piston in such a way as to be rotatable independently of each other; at a tip surface of the piston a fitting recess having a circular base and u-shaped cross section being concavely provided; said circular coupling section corresponding to a cylindrical fitting protrusion that fits into the fitting recess being formed on the backing plate of the friction pad (6,7) with an engagement groove for engagingly arranging the C-clip being concavely provided in the circumferential direction at an outer circumferential surface of the fitting protrusion; the fitting protrusion having the C-clip engagely arranged in the engagement groove being inserted for fitting arrangement into the fitting recess of the piston; and a fitting groove configured to fit the C-clip being arranged on the fitting protrusion being provided in a circumferential direction at the inner peripheral surface of the fitting recess of the piston, such when the fitting protrusion is fitted into the fitting recess the C-clip and the fitting protrusion comes to fit with the fitting groove of the fitting recess. an adjustment bolt mounted on an action part side of a calliper body; a piston provided at a tip of said adjustment bolt; and action part side as well as reaction part side friction pads (6,7) that are adapted to be brought, by a movement of said piston toward a disk rotor, into sliding contact with both side faces of the disk rotor; wherein the adjustment bolt and the piston are formed integrally, and wherein a tip of the piston is fittingly arranged, characterised by a C-clip intervening, on a circular coupling section formed on a backing plate that constitutes a back side of the friction pad (6,7), to connect the friction pad (6,7) and the piston in such a way as to be rotatable independently of each other; at a tip surface of the piston a fitting recess having a circular base and u-shaped cross section being concavely provided; said circular coupling section corresponding to a cylindrical fitting protrusion that fits into the fitting recess being formed on the backing plate of the friction pad (6,7) with an engagement groove for engagingly arranging the C-clip being concavely provided in the circumferential direction at an outer circumferential surface of the fitting protrusion; the fitting protrusion having the C-clip engagely arranged in the engagement groove being inserted for fitting arrangement into the fitting recess of the piston; and a fitting groove configured to fit the C-clip being arranged on the fitting protrusion being provided in a circumferential direction at the inner peripheral surface of the fitting recess of the piston, such when the fitting protrusion is fitted into the fitting recess the C-clip and the fitting protrusion comes to fit with the fitting groove of the fitting recess.