A cap feeding device is for a nap nailer that includes a machine body, a muzzle, a nail feeding device, a nail striking device, and an electronic control device. The cap feeding device includes a cartridge, a cap rail, a cap solenoid valve, and a cap pushing member. The cartridge is adapted for accommodating a plurality of caps. The cap rail is connected to the cartridge, and extends toward the muzzle. The cap solenoid valve is mounted to the cap rail, and includes a valve rod that is drivable by an electromagnetic force to move. The cap pushing member is swingably connected to the valve rod, and is urged by the valve rod to move relative to the muzzle between a first position, in which the cap pushing member is adjacent to the muzzle, and a second position, in which the cap pushing member is distal from the muzzle.