A drug injecting apparatus for use in skin surgery comprising: a syringe for injecting drug into the skin through a needle disposed at an end portion thereof; a transfer guide assembly joined with a cylinder of the syringe in which drug is contained, the transfer guide assembly allowing the cylinder to carry out a reciprocating motion within a limited range according to a direction that drug is injected; an injection assembly mounted at one side of the transfer guide assembly for moving a rod of the cylinder toward the needle in interlock with the transfer guide assembly while rotating by a driving force; and a controlling part mounted at one side of the transfer guide assembly and the injection assembly, the controlling part serving to operate the injection assembly when the transfer guide assembly moves to one end of the limited range in a state where an end portion of the needle gets in contact with the skin and to stop the operation of the injection assembly when the end portion of the needle is separated from the skin and the transfer guide assembly moves to the other end of the limited range, wherein the injection assembly transfers the rod toward the needle as long as the cylinder retracts toward the injection assembly, characterized in that the transfer guide assembly comprises: a bracket on which the cylinder is fixed; a support block mounted on a prop segment mounted at a front end portion of the injection assembly; and a guide rail joined to the bottom of the bracket and coupled with the support block, the guide rail having detents (232, 234) respectively disposed at front and rear end portions thereof, so as to reciprocate the bracket, wherein a distance between the support block, which gets in contact with the detent of one side, and the detent of the other side is equal with the depth that the needle is inserted into the skin. a syringe for injecting drug into the skin through a needle disposed at an end portion thereof; a transfer guide assembly joined with a cylinder of the syringe in which drug is contained, the transfer guide assembly allowing the cylinder to carry out a reciprocating motion within a limited range according to a direction that drug is injected; an injection assembly mounted at one side of the transfer guide assembly for moving a rod of the cylinder toward the needle in interlock with the transfer guide assembly while rotating by a driving force; and a controlling part mounted at one side of the transfer guide assembly and the injection assembly, the controlling part serving to operate the injection assembly when the transfer guide assembly moves to one end of the limited range in a state where an end portion of the needle gets in contact with the skin and to stop the operation of the injection assembly when the end portion of the needle is separated from the skin and the transfer guide assembly moves to the other end of the limited range, wherein the injection assembly transfers the rod toward the needle as long as the cylinder retracts toward the injection assembly, characterized in that the transfer guide assembly comprises: a bracket on which the cylinder is fixed; a support block mounted on a prop segment mounted at a front end portion of the injection assembly; and a guide rail joined to the bottom of the bracket and coupled with the support block, the guide rail having detents (232, 234) respectively disposed at front and rear end portions thereof, so as to reciprocate the bracket, wherein a distance between the support block, which gets in contact with the detent of one side, and the detent of the other side is equal with the depth that the needle is inserted into the skin. a bracket on which the cylinder is fixed; a support block mounted on a prop segment mounted at a front end portion of the injection assembly; and a guide rail joined to the bottom of the bracket and coupled with the support block, the guide rail having detents (232, 234) respectively disposed at front and rear end portions thereof, so as to reciprocate the bracket, wherein a distance between the support block, which gets in contact with the detent of one side, and the detent of the other side is equal with the depth that the needle is inserted into the skin.