Abstract: Provided is a wire connection structure for a three-phase sheath type heater that enables to maintain insulation properties, electrical safety, and reliability, without damaging a wire connection portion, even if an installation location is a high-temperature, high-pressure environment, and enables to flow a large electric current, while suppressing the production cost. A canister 2 made of metal is disposed on the distal end side of three sheath type heating elements 10 in a state that a distal end of each of the sheath type heating elements 10 is inserted through a bottom plate 20. A wire connection plate 3 made of metal is disposed in the canister 2 for star-connection. Distal ends of core wires 11 of the sheath type heating elements 10 are joined to the wire connection plate 3 by welding. An insulating material 4 is compressively filled in the remaining space of the canister.