A tube-joining apparatus capable of stably and reliably joining tubes where liquid is contained and sealed. In a tube joining apparatus, a first clamp (6) and second clamp (7) for pressing and holding tubes (8, 9) are arranged in a contact state. When a second moving mechanism is driven to separate the second clamp (7) from the first clamp (6), the first clamp (6) is slid on the tubes by a shaft (121) supporting the first clamp (6) in a vertically movable manner and is moved from a first position (P1) to a second position (P2). The tubes are squeezed with a pressing force being gradually increased while the tubes are slid between slants (67, 77) of an engagement portion (68) and second engagement portion (78). Residual liquid in the tubes is removed from inside the tubes by the squeezing operation of the first clamp 6. The tubes from which the residual liquid is removed are cut by a cutting plate (41), the tubes are moved by first and second moving mechanisms, and then the tubes are joined.