Abstract: The present invention relates to a gas-insulated current transformer of simple structure for a single-phase or multi-phase switchgear, which transformer can be made in various dimensions and with magnetic cores of various lengths. The transformer comprises at least one support tube carrying three annular cores carrying respective secondary windings. The windings are superposed and disposed coaxially about the tube, and they are held by a clamping strap. The tube and the windings are disposed inside an enclosure defined by two metal plates constituting a bottom closure end plate and a top closure end plate, and by four metal side walls. The end plates are interconnected by link rods disposed in their corners. The two end plates are fixed to the ends of the rods by screws, and the metal side plates are screwed to said rods.