A spray gun includes a nozzle connected to the open end of the spray gun and an air cap having a central passage through which the nozzle extends. The air cap includes symmetrical angular passages and multiple air passages. A back board is located at the back face of the air cap and includes an air outlet portion which includes a central hole and multiple air passages which are independent from the central hole. The nozzle extends through the central hole. Multiple resilient members are located on the back face of the air cap and push the back board to contact the air cap constantly. The air cap includes protrusion on the back face and the back board includes notches in its front face so that when rotating the air cap relative to the back board, the user is acknowledged the angle that the air cap is rotated.