A joint unit comprising a resin-made tube in which a liquid transferring channel extending along an axis is formed and a cross section orthogonal to the axis is round, and a joint structure attached to an end of the resin-made tube, the joint structure including: a main body; a tubular part that is formed in a tubular shape to protrude from the main body along the axis and holds an outer peripheral surface of the resin-made tube; and a protrusion that is formed in a shaft shape to protrude from the main body along the axis and forms, between the protrusion and the tubular part, an insertion groove in which the resin-made tube is inserted, with the protrusion also being inserted into the liquid transferring channel of the resin-made tube, wherein the main body and the protrusion are formed with a coupling channel extending along the axis and coupling the liquid transferring channel and another channel, a tip of the protrusion is disposed at a position closer to the main body than a tip of the tubular part, wherein the protrusion includes a base having an outer diameter Dpo, and a tip portion having an outer diameter that gradually decreases towards the tip, wherein the joint unit is configured so that upon the insertion of the protrusion in the liquid transferring channel, the liquid transferring channel is elastically deformed so that the inner diameter (Dti) of the liquid transferring channel increases up to a size of the outer diameter (Dpo) of the protrusion, wherein the outer diameter (Dto) of the resin-made tube increases due to the increase in inner diameter (Dti) of the liquid transferring channel characterized in that the outer peripheral surface of the resin-made tube is held by the inner peripheral surface of the tubular part. a main body; a tubular part that is formed in a tubular shape to protrude from the main body along the axis and holds an outer peripheral surface of the resin-made tube; and a protrusion that is formed in a shaft shape to protrude from the main body along the axis and forms, between the protrusion and the tubular part, an insertion groove in which the resin-made tube is inserted, with the protrusion also being inserted into the liquid transferring channel of the resin-made tube, wherein the main body and the protrusion are formed with a coupling channel extending along the axis and coupling the liquid transferring channel and another channel, a tip of the protrusion is disposed at a position closer to the main body than a tip of the tubular part, wherein the protrusion includes a base having an outer diameter Dpo, and a tip portion having an outer diameter that gradually decreases towards the tip, wherein the joint unit is configured so that upon the insertion of the protrusion in the liquid transferring channel, the liquid transferring channel is elastically deformed so that the inner diameter (Dti) of the liquid transferring channel increases up to a size of the outer diameter (Dpo) of the protrusion, wherein the outer diameter (Dto) of the resin-made tube increases due to the increase in inner diameter (Dti) of the liquid transferring channel characterized in that the outer peripheral surface of the resin-made tube is held by the inner peripheral surface of the tubular part.