An entrained-bed cylindrical gasifier to which pulverized coal as a raw material and an oxidizer are supplied through one or more burners disposed at the top of the gasifier, wherein each of the burners is composed of a quadruple tube and comprises: a raw material supply line that is the most central region through which the pulverized coal is injected into the gasifier by a carrier gas; a primary oxidizer region that is an annular region provided around the raw material supply line and having formed therein a plurality of primary oxidizer supply holes through which a primary oxidizer is injected toward a region into which the pulverized coal is injected through the raw material supply line, so that the pulverized coal is directed toward the central region; and a secondary oxidizer region that is an annular region provided around the primary oxidizer region having formed therein a plurality of secondary oxidizer supply holes through which a secondary oxidizer is injected toward a region into which the pulverized coal is injected through the raw material supply line, so that the pulverized coal is directed toward the central region, a cooling water region which is the outermost annular region provided around the primary oxidizer region and the secondary oxidizer region and through which cooling water is introduced into the gasifier and discharged from the gasifier, characterized in that when the pulverized coal is high-rank coal having poor reactivity, the oxidizer is injected at an angle of 0° to +20° with respect to the perpendicular direction toward the region into which the pulverized coal is injected through the raw material supply line and consists of the primary oxidizer, when the pulverized coal is low-rank coal having good reactivity, the oxidizer is injected at an angle of -20° to 0° with respect to the perpendicular direction toward the region into which the pulverized coal is injected through the raw material supply line and consists of the primary oxidizer and the secondary oxidizer, the ratio between the primary oxidizer and the secondary oxidizer, which are injected, is controlled such that gasification of the pulverized coal occurs slowly compared to when only the primary oxidizer is supplied, and a reaction region of the gasifier has an aspect ratio (L/D) of 5-10, wherein L and D are the length and diameter of the reaction region, respectively. a raw material supply line that is the most central region through which the pulverized coal is injected into the gasifier by a carrier gas; a primary oxidizer region that is an annular region provided around the raw material supply line and having formed therein a plurality of primary oxidizer supply holes through which a primary oxidizer is injected toward a region into which the pulverized coal is injected through the raw material supply line, so that the pulverized coal is directed toward the central region; and a secondary oxidizer region that is an annular region provided around the primary oxidizer region having formed therein a plurality of secondary oxidizer supply holes through which a secondary oxidizer is injected toward a region into which the pulverized coal is injected through the raw material supply line, so that the pulverized coal is directed toward the central region, a cooling water region which is the outermost annular region provided around the primary oxidizer region and the secondary oxidizer region and through which cooling water is introduced into the gasifier and discharged from the gasifier, characterized in that when the pulverized coal is high-rank coal having poor reactivity, the oxidizer is injected at an angle of 0° to +20° with respect to the perpendicular direction toward the region into which the pulverized coal is injected through the raw material supply line and consists of the primary oxidizer, when the pulverized coal is low-rank coal having good reactivity, the oxidizer is injected at an angle of -20° to 0° with respect to the perpendicular direction toward the region into which the pulverized coal is injected through the raw material supply line and consists of the primary oxidizer and the secondary oxidizer, the ratio between the primary oxidizer and the secondary oxidizer, which are injected, is controlled such that gasification of the pulverized coal occurs slowly compared to when only the primary oxidizer is supplied, and a reaction region of the gasifier has an aspect ratio (L/D) of 5-10, wherein L and D are the length and diameter of the reaction region, respectively.