An automatic retractable syringe includes a tubular body (11) on which a syringe opening (14) is provided a piston body (12) in whose pressing portion a vent hole V A is formed and in whose shaft portion a vent passage (16) passing from the vent hole V A through inside to the front end portion is formed and a spring (17) which returns the pressed piston body (12) to its original position. When the pressing portion is pressed by a thumb or other finger plugging the vent hole V A to move the piston body (12) forward, air is supplied from the syringe opening (14). Subsequently, when the thumb or other finger is released, air flows into the tubular body (11) through the vent hole V A and the vent passage, and the piston body automatically returns to its original position by the spring (17). Therefore, air can be consecutively supplied by repeatedly pressing the pressing portion.
