An insertion device for inserting an injection needle into a tissue including a needle holder carrying the injection needle and a protection device for covering the injection needle after the removal thereof from the tissue wherein the needle holder is mounted to move along the needle axis in relation to the protection device and for insertion of the injection needle the needle holder and protection device are moved more closely together and wherein at least one catch is provided on at least one of the needle holder and protection device, which firmly engages the needle holder with the protection device in an extended relative position. The invention encompasses a catheter head having a base body, a flexible cannula extending from the base body and the insertion device with the protection device.