To provide a manufacturing method of a heat-shrinkable tube and a manufacturing apparatus of a heat-shrinkable tube each capable of stably manufacturing a tube while inhibiting irregularities of the tube diameter.

The provided manufacturing method of a heat-shrinkable tube comprises the following steps. A tube 1 consisting of a resin is heated at or above the softening point of the resin. The diameter of the heated tube 1 is expanded. At the step of expanding the diameter of the tube 1, a gas is introduced into the tube 1 interior, and the tube 1 is transmitted through the interior space 36 of a sizing tube 3 while a compressed state is being maintained within the tube 1 interior. The pressure within the interior space 36 of the sizing tube 3 is measured. The pressure within the tube 1 is adjusted depending on the pressure within the interior space 36 of the sizing tube 3. At the step of transmitting the tube 1 through the interior space 36 of the sizing tube 3, the tube 1 is expanded based on the pressure difference of the pressure of the compressed tube 1 interior and the pressure of the interior space 36 of the decompressed sizing tube 3.