A mechanical disk brake for a bicycle is characterized in a thrust bearing included in a cam mechanism thereof to overcome the problem of a locked disk brake due to an overly large friction as frequently occurs in conventional mechanical disk brakes, and an eccentric force-application arm with an improved geometrical shape to create different arms of force that enables production of an enhanced tail braking force for the mechanical disk brake. The problem of largely reduced braking force occurs in conventional rim brakes in bad weather or in braking over a prolonged time, and the problem of self-locking frequently occurs in the conventional mechanical disk brakes.