Abstract: A trocar assembly includes a cannula, a trocar needle fitted in a lumen of the cannula, a cannula-retaining member having a through-hole for inserting the cannula therein and being provided at a bottom thereof with an adhesive layer for fixing the cannula in place on the skin of a patient. The cannula is adapted to be held in the retaining member by engaging elements between them to permit the cannula to move forward continuously or continually through the through-hole of the retaining member as well as to fix the cannula in a desired position.