Colour television display apparatus in which for correction of isotropic astigmatism a correction current flows through the coil halves of at least one deflection coil unit, which current is substantially a square function of at least one deflection current. As a result a correction quadripolar field is produced. The correction current generator includes passive elements, namely impedances, diodes and transistors operating as switches. The deflection coil halves are toroidally wound on the core.