A carbon material for a negative electrode of a lithium ion secondary battery comprising: particles having an average particle diameter of 5 to 20 μm and having a structure which includes a plurality of stacked plates and is curved into a bow shape, the particles being of calcined coke or graphitized coke obtainable in a method comprising the steps of: subjecting a heavy oil to coking using a delayed coking method at a pressure of 400 to 800 kPa and at 400 to 600°C to form a raw coke material with generation of a hydrogen gas, a hydrocarbon gas having one carbon atom (C1 gas), and a hydrocarbon gas having two carbon atoms (C2 gas), wherein the ratio of the total of the generation rates (mass%) of the hydrogen gas, C1 gas, and C2 gas to the formation rate (mass%) of the raw coke material satisfies the condition: total of generation rates/formation rate = 0.30 to 0.60, pulverizing the raw coke material to obtain a raw coke material powder having an average particle size of 30 μm or less, calcining the raw coke material powder at 1000 to 1500°C for carbonization to obtain calcined coke, and optionally pulverizing and graphitizing the calcined coke at a temperature of 2200 to 2800°C to obtain graphitized coke, wherein, in each of the plates, an average plate thickness is defined as T, an average bow height including the plate thickness is defined as H, and an average length in the vertical direction is defined as L, L/T is 5.0 or more and H/T is from 1.10 to 1.25, and wherein the heavy oil is selected from the group consisting of desulfurized and deasphalted petroleum oil, hydrodesulfurized heavy oil, fluid catalytic cracking bottom oil, vacuum residual oil, coal-liquefied oil, solvent extraction oil of coal, atmospheric residual oil, shale oil, tar sand bitumen, naphtha tar pitch, coal tar pitch, and heavy oils obtained by hydrorefining of the foregoing. particles having an average particle diameter of 5 to 20 μm and having a structure which includes a plurality of stacked plates and is curved into a bow shape, the particles being of calcined coke or graphitized coke obtainable in a method comprising the steps of: subjecting a heavy oil to coking using a delayed coking method at a pressure of 400 to 800 kPa and at 400 to 600°C to form a raw coke material with generation of a hydrogen gas, a hydrocarbon gas having one carbon atom (C1 gas), and a hydrocarbon gas having two carbon atoms (C2 gas), wherein the ratio of the total of the generation rates (mass%) of the hydrogen gas, C1 gas, and C2 gas to the formation rate (mass%) of the raw coke material satisfies the condition: total of generation rates/formation rate = 0.30 to 0.60, pulverizing the raw coke material to obtain a raw coke material powder having an average particle size of 30 μm or less, calcining the raw coke material powder at 1000 to 1500°C for carbonization to obtain calcined coke, and optionally pulverizing and graphitizing the calcined coke at a temperature of 2200 to 2800°C to obtain graphitized coke, subjecting a heavy oil to coking using a delayed coking method at a pressure of 400 to 800 kPa and at 400 to 600°C to form a raw coke material with generation of a hydrogen gas, a hydrocarbon gas having one carbon atom (C1 gas), and a hydrocarbon gas having two carbon atoms (C2 gas), wherein the ratio of the total of the generation rates (mass%) of the hydrogen gas, C1 gas, and C2 gas to the formation rate (mass%) of the raw coke material satisfies the condition: total of generation rates/formation rate = 0.30 to 0.60, pulverizing the raw coke material to obtain a raw coke material powder having an average particle size of 30 μm or less, calcining the raw coke material powder at 1000 to 1500°C for carbonization to obtain calcined coke, and optionally pulverizing and graphitizing the calcined coke at a temperature of 2200 to 2800°C to obtain graphitized coke, wherein, in each of the plates, an average plate thickness is defined as T, an average bow height including the plate thickness is defined as H, and an average length in the vertical direction is defined as L, L/T is 5.0 or more and H/T is from 1.10 to 1.25, and wherein the heavy oil is selected from the group consisting of desulfurized and deasphalted petroleum oil, hydrodesulfurized heavy oil, fluid catalytic cracking bottom oil, vacuum residual oil, coal-liquefied oil, solvent extraction oil of coal, atmospheric residual oil, shale oil, tar sand bitumen, naphtha tar pitch, coal tar pitch, and heavy oils obtained by hydrorefining of the foregoing.