A gas supply apparatus comprising: a mounting portion for mounting a substrate to be processed; and a gas ejector (1, 2, 3, 4, 100) which is provided above said mounting portion and supplies gas from a processing chamber (18, 180) having an opening on a bottom surface to said substrate to be processed, wherein said gas ejector (1, 2, 3, 4, 100) includes: a primary accommodating chamber (11, 110) which temporarily accommodates gas supplied from a gas supply port; said processing chamber (18, 180); and a nozzle portion (10, 20, 30, 40) which is provided between said primary accommodating chamber (11, 110) and said processing chamber (18, 180), said nozzle portion (10, 20, 30, 40has: a first restricting cylinder (13, 13X) being provided at the uppermost portion of said nozzle portion (10, 20, 30, 40) whose opening has a circular cross-sectional shape with a first diameter in plan view, and which supplies the gas in said primary accommodating chamber (11, 110) downward; a second restricting cylinder (14, 14X, 17) being continuously formed with said first restricting cylinder (13, 13X), whose opening has a circular cross-sectional shape with a second diameter in plan view, and which supplies the gas supplied from said first restricting cylinder (13, 13X) to a third restricting cylinder being continuously formed with said second restricting cylinder (14, 14X, 17), whose opening has a circular cross-sectional shape with a third diameter in plan view, and which supplies the gas supplied from said second restricting cylinder (14, 14X, 17) to said processing chamber (18, 180), said second diameter is set to be longer than said first diameter, said third diameter is longer than said second diameter, characterized in that said nozzle portion (10, 20, 30, 40) is a single nozzle portion, said first diameter is set such that pressure difference between said primary accommodating chamber (11, 110) and said processing chamber (18, 180) is not less than 30 times, and said first diameter of said first restricting cylinder (13, 13X) is set to be not greater than 2 mm in diameter and a formation length of said first restricting cylinder (13, 13X) is set to be not greater than 2 mm. a mounting portion for mounting a substrate to be processed; and a gas ejector (1, 2, 3, 4, 100) which is provided above said mounting portion and supplies gas from a processing chamber (18, 180) having an opening on a bottom surface to said substrate to be processed, wherein said gas ejector (1, 2, 3, 4, 100) includes: a primary accommodating chamber (11, 110) which temporarily accommodates gas supplied from a gas supply port; said processing chamber (18, 180); and a nozzle portion (10, 20, 30, 40) which is provided between said primary accommodating chamber (11, 110) and said processing chamber (18, 180), a primary accommodating chamber (11, 110) which temporarily accommodates gas supplied from a gas supply port; said processing chamber (18, 180); and a nozzle portion (10, 20, 30, 40) which is provided between said primary accommodating chamber (11, 110) and said processing chamber (18, 180), said nozzle portion (10, 20, 30, 40has: a first restricting cylinder (13, 13X) being provided at the uppermost portion of said nozzle portion (10, 20, 30, 40) whose opening has a circular cross-sectional shape with a first diameter in plan view, and which supplies the gas in said primary accommodating chamber (11, 110) downward; a second restricting cylinder (14, 14X, 17) being continuously formed with said first restricting cylinder (13, 13X), whose opening has a circular cross-sectional shape with a second diameter in plan view, and which supplies the gas supplied from said first restricting cylinder (13, 13X) to a first restricting cylinder (13, 13X) being provided at the uppermost portion of said nozzle portion (10, 20, 30, 40) whose opening has a circular cross-sectional shape with a first diameter in plan view, and which supplies the gas in said primary accommodating chamber (11, 110) downward; a second restricting cylinder (14, 14X, 17) being continuously formed with said first restricting cylinder (13, 13X), whose opening has a circular cross-sectional shape with a second diameter in plan view, and which supplies the gas supplied from said first restricting cylinder (13, 13X) to a third restricting cylinder being continuously formed with said second restricting cylinder (14, 14X, 17), whose opening has a circular cross-sectional shape with a third diameter in plan view, and which supplies the gas supplied from said second restricting cylinder (14, 14X, 17) to said processing chamber (18, 180), said second diameter is set to be longer than said first diameter, said third diameter is longer than said second diameter, characterized in that said nozzle portion (10, 20, 30, 40) is a single nozzle portion, said first diameter is set such that pressure difference between said primary accommodating chamber (11, 110) and said processing chamber (18, 180) is not less than 30 times, and said first diameter of said first restricting cylinder (13, 13X) is set to be not greater than 2 mm in diameter and a formation length of said first restricting cylinder (13, 13X) is set to be not greater than 2 mm.