A tube holder includes at least a set of clamping members having circular arc-shaped clamping concave portions, a spindle pivotably supporting end portions on one side along the circular arcs of the clamping members in a state where the clamping concave portions facing curvature center sides of the respective circular arcs face each other, and a biasing member pivoting and biasing end portions of the other side along the circular arc of the clamping member in a direction of mutual approaching. The clamping member is formed such that an inscribed circle formed between facing surfaces of the clamping concave portions is smaller than a virtual circle formed by extension of the circular arcs of the clamping concave portions in a state where a space between the other end portions is closed and the clamping concave portions are disposed on the same virtual circle formed by extension of the circular arcs in a state during opening and closing where the clamping members are pivoted and the end portions on the other side are moved close to and away from each other.