To provide a box body for heating by a microwave oven, which houses so-called retort foods contained in a bag body, and can be heated by a microwave oven under a state wherein self-standing stability is imparted while housing the foods contained in the bag body, and of which the material cost is low, and of which the process is simple.

For this parallelepiped shape box body 1 of which the front and the rear are flat, on side surface plates 4 and 4 on the front and the rear, a folding into valley-shape line (a) which connects a point A and a point A, folding into ridge-shape lines b and b which respectively connect the points A and A and points B and B, a folding into ridge-shape line c which connects the point B and the point B, and folding into ridge-shape lines d and d which respectively connect the points B and B and the lower ends of the right and left ends are respectively provided. Also, on side surface plates 5 and 5 on the right and the left, a folding into ridge-shape line e which connects the point A and the point A is respectively provided. In addition, folding into valley-shape lines f and f which connect the points B and B on the front side surface plate 4 and the points B and B on the rear side surface plate 4 through the side surface plate 5 respectively are provided. Then, on the folding into ridge-shape lines c and c, U-shape leg pieces 9 and 9 are respectively provided.