To provide a simple steamer easily performing the processing of steaming an article.

The steamer is provided with an outer container A whose upper surface side is opened, an inner container B whose upper surface side is opened, constituted so as to form air holes 5 on an article mounting surface part 4 serving also as a bottom surface on which a food material F is to be mounted and to form a clearance 3 between the bottom surface of the outer container A and the article mounting surface part 4 in the state of being positioned inside the outer container A and positioned inside the outer container A, and a liquid storage body C arranged in the clearance 3 formed below the article mounting surface part 4 storing the prescribed amount of distilled water 9. At the time of being heated by microwaves, the distilled water 9 stored in the liquid storage body C becomes steam and the steam is supplied through the air holes 5 to a space above the article mounting surface part 4.