AbstractA design and related studies of equilibrium field control coil system of TPE-RX reversed field pinch (RFP) machine are described. Here the equilibrium field control coil system stands for the coils to produce poloidal magnetic field necessary for the plasma equilibrium condition. The configuration and the number of turns of the equilibrium field control coil system were designed so as to minimize the field error for reducing the plasma–wall interaction, especially at the shell gap of the thick metal shell. The design method of the equilibrium field control coil system taking account of an iron core with two yokes and the thick metal shell with the poloidal shell gap is described. As a result of the design of the equilibrium field control coil system, field error at the plasma surface is less than 1.0%. The field error can be canceled for wide range of the plasma equilibrium condition by adding the compensatory vertical field. Construction of TPE-RX was successfully completed at the end of 1997 and the coil system showed the expected performances.