To provide a fluid heater capable of thermally insulating the ambience of heater elements in a more effective manner and capable of reducing a load acting on screws for presser use fixing.

This fluid heater is equipped with a pair of heater element support members 7, 8 confrontingly disposed in a cylindrical heater body 1, a plurality of heater elements 3 provided in the heater body 1 with their both end parts supported by the heater element support members 7, 8, a tubular thermal insulation member 9 provided between the heater element support members 7, 8 for thermally insulating the ambience of the heater elements 3, and a tubular pressure member 10 for fixing the thermal insulation member 9 by pressing it against an inner circumferential surface of the heater body 1, and characterized by having an inner tube member 12 weldable to the heater element support members 7, 8, provided between the pressure member 10 and the heater body 1.