Abstract: A disk brake includes a plurality of cylinders for slidably receiving pistons for pressing a pad. Each of the cylinders has a main portion for supporting the piston, and an annular groove provided at the bottom of the main portion with a diameter larger than that of the inner cylindrical surface of the main portion. Each pair of adjacent cylinders communicate with each other through a communicating hole that extends from the inner wall of the main cylindrical portion of one cylinder to the annular groove of the other cylinder through the annular groove of the one cylinder. A drill for making such a hole thus need not interfere with the inner wall of the one cylinder at the open-end portion thereof.