A cannula retractable medical collection device includes a cannula mount inserted into and axially slidable relative to a rear larger-diameter wall portion of a barrel, a double-ended needle cannula including a rear needle segment extending into an accommodation chamber in the cannula mount for pricking a stopper of a collection vial, and a front needle segment secured to the cannula mount by a needle hub. The front needle segment extends outwardly of the barrel in a position of use, and retreats inwardly and rearwardly of the barrel in a disposal position when the cannula mount is in the front and rear positions, respectively. A releasably retaining member includes a retaining hole formed in the larger-diameter wall portion, and a radially extending engaging peg engageable in the hole. An actuator is operable to disengage the peg from the hole so as to permit axial movement of the cannula mount.