An improved disk brake which provides both low dragging torque and good pedal feeling even on ABS-equipped vehicles with which the working fluid pressure is around or over 140 kgf/cm.sup.2. The disk brake has a piston seal fitted in a groove formed in the cylinder. The piston seal is deformed when the brake piston is advanced by fluid pressure to press the pad and retracts the piston by its spring-back force when the fluid pressure is released. The width W of chamfer provided at edge of the seal groove is set to 1.0 mm or over and the hardness of the piston seal is set to 75.degree. IRHD or over.