A tube joining device that is configured to fuse an end of a first tube and an end of a second tube by a plate-shaped cutting member that is configured to be heated, and to replace the fused end of the first tube and the fused end of the second tube and to join the fused ends in an aseptic condition, comprising: a first tube holding portion that is capable of holding one tube between the first tube and the second tube; a second tube holding portion that is capable of holding the other tube between the first tube and the second tube; a tube superimposing portion that is configured to cause the first tube holding portion and the second tube holding portion to relatively approach each other to dispose the one tube and the other tube in a superimposed manner; and a switching mechanism that is capable of switching holding of the other tube by the second tube holding portion and release of the holding, wherein the switching mechanism is configured to apply a biasing force for maintaining a state in which the other tube is held to the second tube holding portion, and to apply a biasing force for maintaining a state in which the holding of the other tube is released to the second tube holding portion in accordance with the relative approaching of the first tube holding portion and the second tube holding portion, wherein the second tube holding portion includes a first claw portion and a second claw portion which are capable of approaching each other or capable of being separated from each other, and a support portion that rotatably supports the first claw portion and the second claw portion, the switching mechanism includes, a first biasing member that is configured to apply a biasing force to the first claw portion, and characterized in that the switching mechanism further includes a second biasing member that is configured to apply a biasing force to the second claw portion, and the first biasing member and the second biasing member are configured to apply the biasing forces toward directions of closing the first claw portion and the second claw portion in a state in which the first tube holding portion is separated from the second tube holding portion, and to apply the biasing forces toward directions of opening the first claw portion and the second claw portion in a state in which the first tube holding portion and the second tube holding portion approach each other. a first tube holding portion that is capable of holding one tube between the first tube and the second tube; a second tube holding portion that is capable of holding the other tube between the first tube and the second tube; a tube superimposing portion that is configured to cause the first tube holding portion and the second tube holding portion to relatively approach each other to dispose the one tube and the other tube in a superimposed manner; and a switching mechanism that is capable of switching holding of the other tube by the second tube holding portion and release of the holding, wherein the switching mechanism is configured to apply a biasing force for maintaining a state in which the other tube is held to the second tube holding portion, and to apply a biasing force for maintaining a state in which the holding of the other tube is released to the second tube holding portion in accordance with the relative approaching of the first tube holding portion and the second tube holding portion, wherein the second tube holding portion includes a first claw portion and a second claw portion which are capable of approaching each other or capable of being separated from each other, and a support portion that rotatably supports the first claw portion and the second claw portion, the switching mechanism includes, a first biasing member that is configured to apply a biasing force to the first claw portion, and characterized in that the switching mechanism further includes a second biasing member that is configured to apply a biasing force to the second claw portion, and the first biasing member and the second biasing member are configured to apply the biasing forces toward directions of closing the first claw portion and the second claw portion in a state in which the first tube holding portion is separated from the second tube holding portion, and to apply the biasing forces toward directions of opening the first claw portion and the second claw portion in a state in which the first tube holding portion and the second tube holding portion approach each other.