The invention relates to a nail cap support device, and belongs to equipment for producing nail cap supports for big rimmed caps. The nail cap support device mainly solves the technical problems of time and labor waste, low efficiency and poor quality in the conventional manual rivet cap supports. According to the technical scheme, the nail cap support device comprises a frame, a bedplate, a left foot valve, a right foot valve and a main machine body, wherein the main machine body consists of a main frame, a pressure gun cylinder, a lock nut, a main shaft, a sliding block, a main shaft sleeve, a connecting plate, a pneumatic code nail gun, a cap support seat, a cap support positioning block and a trigger cylinder; the pressure gun cylinder is arranged on the upper part of the main frame, a piston rod of the pressure gun cylinder is connected with the main shaft through a screw buckle, the main shaft sleeve is arranged outside the main shaft, and the sliding block is arranged on the middle part of the main shaft and positioned in a slipway of the main shaft sleeve; the lower end of the main shaft is provided with the connecting plate which is connected with the top of the pneumatic code nail gun, and the cap support seat is arranged on a bracket on the lower part of the main frame; and the cap support positioning block is arranged on the inclined plane of the rear part of the cap support seat.