Provided is an automatic
syringe, comprising: a housing (1), a
needle guard cover (2), a push rod (3), a sounding cylinder (4), an inner tube (5), a release ring (6), a driving elastic member, and a resetting elastic member. During use, a needle cylinder (9) is fixed in the housing (1); a needle head (91) protrudes from the front of the housing (1); the
needle guard cover (2) is retractably attached to the housing (1); the
needle guard cover (2) can push the release ring (6) to slide toward the rear end of the housing (1); after the release ring (6) moves to the rear end, a first clip (55) of the inner tube (5) releases the snap-fit position-limiting of the push rod (3); the push rod (3) pushes a
piston (93) under the action of the driving elastic member to inject the liquid in the needle cylinder (9) into a part of the body to be injected, achieving automatic injection. After the injection is complete, the sounding cylinder (4) disengages from the position-limiting of the inner tube (5) and slides toward the rear end of the housing (1), in order to issue a
signal that the injection is complete. The automatic
syringe of the present solution uses eight component parts to achieve the automatic injection function of the pre-filled needle cylinder; in comparison with the prior art, the present solution has a simple structure and a small number of components, is simple in its principle of mechanism action, and is highly reliable.