A solenoid valve and an automatic document feeder using the solenoid valve are provided. The solenoid valve includes a valve body, a valve spindle, a spring, a ring-shaped groove and muffling ring. The ring-shaped groove is sheathed around the valve spindle. The muffling ring is disposed within the ring-shaped groove. When the valve body is magnetized to magnetically attract the valve spindle, the valve spindle is moved within the valve body, and the muffling ring collides with the recess inner wall, thereby reducing collision noise.