A connection device includes a tube that is branched to two passages from a branch portion and includes a first and second branch tubes provided on one end side as a liquid-feeding destination, a first protruding plate that includes, on another end side, first another end edge provided in a direction orthogonal to an axis line of the first branch tube and that is provided so as to protrude from an outer circumference portion of the tube, and a second protruding plate that is provided so as to face the first protruding plate across the tube and protrude in a diameter direction of the tube and that includes, on the other end side, second another end edge provided so as to be orthogonal to an axis line of the second branch tube.
