PURPOSE: To efficiently adsorb deposit in a steam generator, to maintain the efficiency of the deposit adsorption for a long period, and to facilitate the maintenance of the steam generator.

CONSTITUTION: A steam generator 11 comprises a container body 12 to store water, and a heat source 14 disposed at the inner bottom of the container body 12, and heating water therein to generate steam. Four plate-form deposit- adsorbing beds 27 are disposed in such a manner to be immersed in water in the container body 12 at equal intervals from above. In convection chambers 28 partitioned by the respective deposit adsorbing beds 27, a convection is generated by the heat source 14. This constitution brings quantities of water into contact with the surface of fibers, having a high zeta potential, constituting the deposit-adsorbing floor 27, and separates out mineral ion in water as deposit, and heats the whole water in the container body 12 to efficiently generate steam.