A method for manufacturing polycrystalline silicon, in which a plurality of silicon seed rods stood in a reaction furnace is heated and polycrystalline silicon is deposited on surfaces of the silicon seed rods by a raw material gas ejected from gas ejection ports located in an inner bottom part of the reaction furnace, the method comprising a step of depositing polycrystalline silicon on the plurality of silicon seed rods stood in the reaction furnace, wherein the step of depositing polycrystalline silicon comprises: a stabilizing step of deposition wherein a velocity of ejecting the raw material gas from the gas ejection ports is gradually increased in a first stage of the deposition of the polycrystalline silicon to stabilize the posture of the silicon rods until a diagonal length L of the deposited polycrystalline silicon S reaches 2 to 3 times of a diagonal length d of the silicon rods in a rectangular shape in cross sections thereof; a shaping step wherein, after the stabilizing step of deposition, first the ejection velocity is increased at an increasing rate higher than that in the stabilizing step and then the ejection velocity is gradually increased at a rate lower than the increasing rate, to change the silicon seed rods from an angled shape to an round shape until an outer diameter of the deposited polycrystalline silicon S reaches to 6 to 10 times of the diagonal length of the silicon rods in cross sections thereof; and a growing step wherein, after the shaping step, the ejection velocity is made slower than that at the end of the shaping step, to accelerate growth of the silicon rod for 10 to 60 minutes; and wherein, a plurality of the gas ejection ports is branched from a gas supplying pipe, and in the shaping step, an ejection velocity from a part of gas ejection ports is increased by closing the other of the plurality of gas ejection ports; the velocities of ejecting the raw material gas in the stabilizing step, the shaping step, and the growing step, are controlled by controlling the opened/closed state of the gas ejection ports; in the stabilizing step, the velocity of the ejecting the raw material gas is increased by closing 5% to 15% of the ejection ports; the duration required for the shaping step corresponds to 20 to 35% of the total duration of the deposition of the polycrystalline silicon; in the shaping step, 30% to 55% of the gas ejection ports are closed; and in the growing step, the velocity of ejecting the raw material gas is decreased by making the number of closed gas ejection ports less than that in the shaping step and 10% to 20% of the gas ejection ports are closed. a stabilizing step of deposition wherein a velocity of ejecting the raw material gas from the gas ejection ports is gradually increased in a first stage of the deposition of the polycrystalline silicon to stabilize the posture of the silicon rods until a diagonal length L of the deposited polycrystalline silicon S reaches 2 to 3 times of a diagonal length d of the silicon rods in a rectangular shape in cross sections thereof; a shaping step wherein, after the stabilizing step of deposition, first the ejection velocity is increased at an increasing rate higher than that in the stabilizing step and then the ejection velocity is gradually increased at a rate lower than the increasing rate, to change the silicon seed rods from an angled shape to an round shape until an outer diameter of the deposited polycrystalline silicon S reaches to 6 to 10 times of the diagonal length of the silicon rods in cross sections thereof; and a growing step wherein, after the shaping step, the ejection velocity is made slower than that at the end of the shaping step, to accelerate growth of the silicon rod for 10 to 60 minutes; and wherein, a plurality of the gas ejection ports is branched from a gas supplying pipe, and in the shaping step, an ejection velocity from a part of gas ejection ports is increased by closing the other of the plurality of gas ejection ports; the velocities of ejecting the raw material gas in the stabilizing step, the shaping step, and the growing step, are controlled by controlling the opened/closed state of the gas ejection ports; in the stabilizing step, the velocity of the ejecting the raw material gas is increased by closing 5% to 15% of the ejection ports; the duration required for the shaping step corresponds to 20 to 35% of the total duration of the deposition of the polycrystalline silicon; in the shaping step, 30% to 55% of the gas ejection ports are closed; and in the growing step, the velocity of ejecting the raw material gas is decreased by making the number of closed gas ejection ports less than that in the shaping step and 10% to 20% of the gas ejection ports are closed.