An injection pen comprises a circularly pushing device (1) and a vial housing (2) and is used to combine a medication vial (3) with a needle (4). The circularly pushing device (1) comprises a jointing member (10) a spiral sleeve (20) a spiral duct (30) a spirally pushing tube (40) a threaded connection shrink ring (50) a propelling lever (60) a one way ratchet ring (70) and an injection operation member (80). During the injection the one way ratchet ring (70) on a push rod (81) is jointed with a one way ratchet groove portion (46) of the spirally pushing tube (40) so as to restrain the rotation directions of the push rod (81) and the spirally pushing tube (40) the propelling lever (60) cannot be rotated due to the limit of the jointing member (10).
