Abstract: The present invention provides a microwave radiating device which treats a radiated material by microwave irradiation; and further provides a method of producing a sugar ingredient from a plant material. The microwave radiating device of the present invention is equipped with an irradiating means which has a microwave radiating source, and containers which accept radiated material inside. Further, the container of the device has supply means which provides radiated material to the container, and discharge means which discharges radiated material from the container, and a microwave receiving section which makes microwaves that irradiate from radiating means, penetrate into the container through the medium of dielectric material. Further, there is provided at least one layer that is composed of non-dielectric material, between the atmosphere of the inner side and the outer side of the container. Yet, irradiating means and the above container are connected in a removable mode.