PROBLEM TO BE SOLVED: To provide a treating liquid heating device of a substrate treating device in which the leakage of treating liquid is surely prevented. SOLUTION: A treating liquid heating device 2 is provided with a housing 25 made of stainless steel consisting of a cylindrical sidewall 22, a bottom wall 23 and a flange 24, and a disk-like cover 26 made of stainless steel, just like the housing 25. The peripheral part of the cover 26 and the flange 24 of the housing 25 are gastightly abutted with each other by action of eight sets of screw threads 27 and nuts 30. A heater 28 is attached to the cover 26. The heater 28 has the form of bends in which a pair of base end parts are fixed to the cover 26 with the cover 26 and the housing 25 being abutted so that it may be housed in a gastight chamber formed by the cover 26 and the housing 25.