A tubular heater includes a continuous heat-generating resistance element formed in a predetermined pattern on one surface of a tubular insulating substrate, and first and second lead wires connected opposite ends of the heat-generating resistance element and extending from one end of the tubular insulating substrate in a common axial direction of the tubular insulating substrate. The first and second lead wires are disposed in diametrically opposed relation to each other about a central axis of the tubular insulating substrate.