An impression tray for an upper jaw comprising: a bottom portion, which is formed as a U-like shaped approximately flat surface with an approximately uniform width, an outer wall, which is provided upright from an outer side of the bottom portion via a circular arc shaped portion, said outer side including the end portions of the U-like shaped portion and said outer wall having its height reduced gradually toward the end portions of the U-like shaped portion of the bottom portion; a bulge portion which bulges from an inner side of said bottom portion so as to form a smooth curved surface and occludes the inner side space between said U-like shaped bottom portions; the impression tray being made of a plastic, wherein a rim having a height of 0.01 to 1 mm is provided along an upper end of said outer wall, for forming an undercut portion below the rim on the bottom portion side of said outer wall, wherein first elongated through holes are formed in said outer wall which does not include the end portions of the U-like shaped portion of the bottom potion, wherein each of said first elongated through holes reaches the bottom portion from a portion just below the rim vertically to the rim and has a width of 1.5 to 4.0 mm, wherein a distance between the adjacent first elongated through holes is from 2 to 5 times the width of the first elongated through hole and is uniform, wherein second elongated through holes are formed in said bulge portion, wherein each of said second elongated through holes reaches the bottom portion and has the same width as the width of the first elongated through hole, and wherein the second elongated through holes are provided: - at positions corresponding to the first elongated through hole except at a front teeth portion side in said bulge portion, and - in a section positioned at the center of the front teeth portion side, wherein circular through holes are formed in said bottom portion at a center of the distances of adjacent first elongated through holes wherein each circular through hole has a diameter of 3 to 6 mm, and wherein elongated end portion side through holes each of which has a width of 1.0 to 3.0 mm and a length of 5 to 15 mm are provided on the bottom portion: - on a line which connects the bottom portion of the respective first and second elongated through holes (5, 6) positioned closest to the end portions of the U-like shaped portion or - in the sides which are closer to the end portions of the U-like shaped portion than said line, and wherein said through holes are provided on the end portion side in the center of said bulge portion. a bottom portion, which is formed as a U-like shaped approximately flat surface with an approximately uniform width, an outer wall, which is provided upright from an outer side of the bottom portion via a circular arc shaped portion, said outer side including the end portions of the U-like shaped portion and said outer wall having its height reduced gradually toward the end portions of the U-like shaped portion of the bottom portion; a bulge portion which bulges from an inner side of said bottom portion so as to form a smooth curved surface and occludes the inner side space between said U-like shaped bottom portions; the impression tray being made of a plastic, wherein a rim having a height of 0.01 to 1 mm is provided along an upper end of said outer wall, for forming an undercut portion below the rim on the bottom portion side of said outer wall, wherein first elongated through holes are formed in said outer wall which does not include the end portions of the U-like shaped portion of the bottom potion, wherein each of said first elongated through holes reaches the bottom portion from a portion just below the rim vertically to the rim and has a width of 1.5 to 4.0 mm, wherein a distance between the adjacent first elongated through holes is from 2 to 5 times the width of the first elongated through hole and is uniform, wherein second elongated through holes are formed in said bulge portion, wherein each of said second elongated through holes reaches the bottom portion and has the same width as the width of the first elongated through hole, and wherein the second elongated through holes are provided: - at positions corresponding to the first elongated through hole except at a front teeth portion side in said bulge portion, and - in a section positioned at the center of the front teeth portion side, - at positions corresponding to the first elongated through hole except at a front teeth portion side in said bulge portion, and - in a section positioned at the center of the front teeth portion side, wherein circular through holes are formed in said bottom portion at a center of the distances of adjacent first elongated through holes wherein each circular through hole has a diameter of 3 to 6 mm, and wherein elongated end portion side through holes each of which has a width of 1.0 to 3.0 mm and a length of 5 to 15 mm are provided on the bottom portion: - on a line which connects the bottom portion of the respective first and second elongated through holes (5, 6) positioned closest to the end portions of the U-like shaped portion or - in the sides which are closer to the end portions of the U-like shaped portion than said line, - on a line which connects the bottom portion of the respective first and second elongated through holes (5, 6) positioned closest to the end portions of the U-like shaped portion or - in the sides which are closer to the end portions of the U-like shaped portion than said line, and wherein said through holes are provided on the end portion side in the center of said bulge portion.