PURPOSE: To provide the mold for working the tube-end of a synthetic resin-tube in which the cooling time of the mold is reduced, and the working efficiency of tube end-working is improved.

CONSTITUTION: The first mold 2 is which an outer shell 21 and an inner shell 22 are alternately arranged, while a conical thruster 23 is circularly wound thereon, and then the outer shell 21 and the inner shell 22 are moved in a radial direction by the axial movement of the thruster 23, whereby their diameters are reduced or expanded, is provided. In the mold for working the tube-end provided with such first mold 2, the inside-cooling mechanism capable of discharging cooling medium in the first mold 2 is composed of the medium path 40 provided in the guiding shaft 4 guiding the movement of the thruster 23 and the pump which is not shown in the figure.