A method of manufacturing a brake disk made of gray cast iron is disclosed. The method includes casting a disk body using gray cast iron containing 3.1 wt % to 3.7 wt % of C; machining a surface of the cast disk body; nitriding the disk body by exposing the machined surface to a temperature in the range of 540° C. to 580° C. for 50 min to 70 min, and coating the nitrided disk body.