PURPOSE: To obtain a continuous heater which effectively heats and transports water, by providing a water tube with a first zone for heating water to below the boiling point, a second zone for heating the water to the boiling point, a third zone for heating the water until steam bubbles are formed, and a fourth zone for reheating the water.

CONSTITUTION: In this continuous heater, the following heating distribution is assigned to a heater tube 2 over the entire extent thereof. That is, a water tube 1 is provided with a vertical inflow end 3, a first zone which forms an arcuate bending portion 4 of the water tube for intensively heating water below the boiling point, then a second zone which forms a tube member 5 of the water tube slightly rising toward an outflow end for heating the water less intensively, successively a third zone which forms an arcuate bending portion 6 adjacent to the second zone for intensively heating the water until steam bubbles are vigorously formed, and finally a fourth zone which forms a vertical outflow end 7 for reheating the water less intensively. Such a configuration and the spatial arrangement of the water tube zones described above can remarkably improve the efficiency of such a continuous heater.