Abstract: A drug solution injector comprises a needle tube having a sharp needlepoint, a bottomed outer cylinder arranged on the base end side of the needle tube and having an inside space communicable with the inside of the needle tube, a gasket slidable within the outer cylinder, a drug solution in the space formed by the outer cylinder and the gasket, a support member supporting the needle tube and having a flow channel communicating with the inside of the needle tube, an operation mechanism permitting selection between a communicated state wherein the inside of the needle tube and the inside of the outer cylinder communicate with each other through the flow channel and a blocked state wherein the communication is blocked by rotating the support member, and an exposure preventer for preventing exposure of the needlepoint.