The invention relates to a practical sheet of good heat resistance to the heating of a microwave, excellent rigidity and impact resistance, while the application consumption of petroleum resin is reduced. The sheet is obtained through pressing an external layer on each side of a substrate layer, wherein the substrate layer is composed of a resin composition A. The resin composition A at least comprises the following components by mass: 20-60% polylactic resin, 10-60% polyolefin resin and 20-50% inorganic fillings. The external layers are composed of a resin composition B. The resin composition B at least comprises 40-100% polyolefin resin by mass.