PURPOSE: To manufacture a high current density wire-rod and a high current density coil by rolling or drawing an oxide superconductor in such a condition that it is enveloped in a metallic sheath, giving CIP treatment to the rolled or drawn superconductor and then heat-treating the resultant superconductor.

CONSTITUTION: Press load required for cold isotropic pressure-giving CIP treatment is chosen to have preferably not less than 1 ton/cm2, and a temperature applied to heat treatment is chosen to have a range between 700 and 900°C. The CIP treatment is applied to an oxide superconductor enveloped in a metallic sheath so that the degree of denseness of the oxide superconductor can be upgraded to improve the current density thereof. Also for the manufacture of a coil, the CIP treatment is employed to pressurize the superconductor in an equi-direction so that the superconductor can be equally pressurized even if it is preformed in the shape of a coil. Whereby the advantage of the CIP treatment can be employed efficiently to readily manufacture a coil of excellent properties.