A drug administration mechanism, a method of using the drug administration mechanism, and a pump unit for the drug administration mechanism are disclosed. The drug administration mechanism comprises a body and a pump unit (3) installed on the body. The pump unit (3) comprises a pump (31), a suction-side tube (333), a discharge-side tube (334) and a relief tube opening/closing valve (36, 36a). The pump (31) is utilized for suctioning a drug from a drug container and discharging the drug to a patient by repeatedly increasing and reducing the volume of a feeder portion. The suction-side tube (333) is extended from the pump (31) toward the drug container. The discharge-side tube (334) is extended from the pump (31) toward the patient. The relief tube (35, 35a) comprises a first end (351) connected to the discharge-side tube (333) and a second end (352) positioned in a portion that has a pressure less than the pressure inside the discharge-side tube during administering of the drug. The relief tube opening/closing valve (36, 36a) is utilized for opening and closing the relief tube (35, 35a).本發明係關於一種給藥機構、給藥機構之使用方法、以及給藥機構用幫浦單元；該給藥機構包含：本體；及安裝於該本體之幫浦單元(3)；且幫浦單元(3)包含：幫浦(31)，其藉由反覆擴大/縮小進行送液的部分之容積，而自藥劑容器吸引藥劑並向患者噴出；吸引側配管(333)，其自幫浦(31)向藥劑容器側延伸；噴出側配管(334)，其自幫浦(31)向患者側延伸；釋放配管(35，35a)，其一端(351)連接於上述噴出側配管(333)，另一端(352)位於在藥劑投予時成為較噴出側配管內之壓力低壓之部分；及釋放配管開閉閥(36，36a)，其開閉釋放配管(35，35a)。
